One of the things you will have probably already heard about training plans is the importance of putting it down on paper, and keeping a record of what you do. You may also have heard of things like training cycles, plateaus, cross-training and so on. I thought I'd set out an example of how to put all of this into practice yourself, with just a spreadsheet. It can seem complicated when you don't see the whole process, it's actually pretty simple. Once you've got the basics, you can do it easily for any form of training. This is taken from elite athlete preparation, but the basic insights apply to anyone. I've been using it for years, both for myself and for training rowing crews.
For all of the below, we're planning for a training period of 6 months, assuming your target (race or training) starts at the 6 month point.
Training Cycles
Cycles just mean you want to split your total training period into shorter focus periods. Each focus is a general area of fitness: Endurance, Speed, Strength, Flexibility (it could also be specific to your sport, like Technique or Hill fitness). Each focus period wants to be minimum 4 weeks. You should aim for 6-8 weeks (4 weeks is really only for multi-discipline sports where you need many different focuses, like triathlon or pentathlon).
There is a pattern we want to achieve for each cycle, which looks like this:

The left axis is quantity, the bottom axis is quality. For the first quarter of the cycle, you want a high quantity of activity, but don't worry about quality. From quarter 2, you then drop it right down to low quantity, and build up until the last quarter is both high quantity and high quality. Quality * Quantity is often called training Load. The blue line of the graph shows the pattern of load you put yourself under through a cycle. The reason for doing this is that studies have shown athletes improve quickest from this pattern: you put yourself under moderate load to start, then drop it right down and build up slowly to max load. Then you start another cycle with a different focus. This eliminates the tendency to plateau in training.
This is basically the same as the 80/20 rule that @PhysMan has outlined, it just puts some structure to it.
A draft 6-month plan of training cycles might look like this:
MONTHS 1-2 STRENGTH
MONTHS 2-3 ENDURANCE 1
MONTHS 4-5 SPEED
MONTHS 5-6 ENDURANCE 2
Linking Cycles
At the end of each cycle, you add a short rest period (about 4 days), which can include active rest, such as very gentle, long jogs, walks or swimming. You do this by slightly shortening the final week of the cycle. The next cycle then starts again with the same pattern, but focusing on a different activity or quality.
Understand that in all training, gains come at least 2 weeks after you have made them. That is how long it takes for your body to develop. So if you have just been training hard for 6 weeks, you could sit on your ass for the next two weeks and still perform better than today the next week (obviously, two weeks after that, you might drop off again though). This is why athletes take long active rest periods before important races.
Planning a cycle
Lets say your cycle is 6 weeks. Break that into individual weeks, following the graph above.
Week 1 - High quantity, Low quality (Medium load)
Week 2 - Low quantity, low quality (Low load)
Week 3 - Low quantity, medium quality (Low load)
Week 4 - Medium quantity, Medium quality (Medium load)
Week 4 - Medium quantity, High quality (Medium load)
Week 6 - High quantity, High quality (High load)
What varies, and can often be confusing, is defining quality. Quantity is fairly easy to define - reps, time spent, distance. Quality is more difficult. I usually read quality as "whatever I would be doing in the real event". Note that for most of the cycle, you aren't doing these kinds of session. It's only really the last week (which remember, is shorter to allow for a rest period) when you are consistently doing your hardest sessions. Also note: most sports do this differently, they add at least one high quality session a week. The example I'm using here is for endurance sports or competitions where you have to perform over a long period, sometimes several days. I'm using that because that is what matches most closely with P-Coy, which is 2 weeks of high performance. Ultimately, how you decide what is quality is down to you. The important part is to keep it consistent.
A training focus doesn't mean you only do that activity - for a strength focus, you don't just lift weights. But developing strength is the purpose of that focus, and everything else is a secondary activity. You prioritise the focus. So your main sessions in any given week will be weights, and your secondary and active rest sessions will be speed or endurance. This is what eliminates the tendency to plateau - during a Strength focus, you may feel like you aren't doing enough running, but that means you are "running rested" for the speed or endurance focus that comes next. You will see from my full example below that much of the activity you do isn't necessarily the focus activity. This is what cross-training means, and is also a contributor to the 80/20 rule (because a lot of the 80 isn't your race sport).
Weekly session pattern
Exactly how you plan your weekly sessions varies a lot, depending on what you are training for. When I've been at full training capacity for military fitness, it's 2-3 sessions a day, 5 days a week. That is a maximum. If you are just starting, do half that. Also, look at the example below, and you will see that most of those 2-3 sessions are really low rent - they should be enjoyable. For example, in the Strength section of the example, a lot of what I was doing was gentle sculling (single rowing) in the middle of summer. That's a pretty unchallenging, enjoyable activity, more sports tanning than training. It was a form of active rest and technical development. It had no direct relation to my training purpose (endurance fell running), but complemented my focus (as an upper body activity).
For P-Coy or endurance sports, I've found a 5-day on, 2-day rest pattern works best. This is simply because you are preparing your body for 5 days on. For single race events, a training/rest split of 3/1/2/1 is often used. Never skimp on the rest days. HOWEVER, a useful trick is to do active rest on one of your rest days. For your active rest session, do an activity from your next upcoming cycle. So in my example, during my Strength cycle, my active rest was long, slow jogs, in preparation for the Endurance running cycle next. This ensures you don't overtax your focus activity, but also maintain your overall fitness and prevent decline.
Pre-race period
If you are training for a race in 6 months, you also add a pre-race period. This should be at least 1 week, but can be as much as 2 weeks (see the point about gains above). During the pre-race period you conduct active rest. This means: flexibility, stretching, and long, slow versions of your race activity. One of the best uses of this period is to explore race routes. If you're doing a fell race, walk the route, perhaps with some light jogging.
Remember the rule of active rest is that you should never be working hard - if you are, even if you feel fine, slow it down. You need to be as disciplined about your rest sessions as you are about your maximum effort sessions.
1/2
For all of the below, we're planning for a training period of 6 months, assuming your target (race or training) starts at the 6 month point.
Training Cycles
Cycles just mean you want to split your total training period into shorter focus periods. Each focus is a general area of fitness: Endurance, Speed, Strength, Flexibility (it could also be specific to your sport, like Technique or Hill fitness). Each focus period wants to be minimum 4 weeks. You should aim for 6-8 weeks (4 weeks is really only for multi-discipline sports where you need many different focuses, like triathlon or pentathlon).
There is a pattern we want to achieve for each cycle, which looks like this:

The left axis is quantity, the bottom axis is quality. For the first quarter of the cycle, you want a high quantity of activity, but don't worry about quality. From quarter 2, you then drop it right down to low quantity, and build up until the last quarter is both high quantity and high quality. Quality * Quantity is often called training Load. The blue line of the graph shows the pattern of load you put yourself under through a cycle. The reason for doing this is that studies have shown athletes improve quickest from this pattern: you put yourself under moderate load to start, then drop it right down and build up slowly to max load. Then you start another cycle with a different focus. This eliminates the tendency to plateau in training.
This is basically the same as the 80/20 rule that @PhysMan has outlined, it just puts some structure to it.
A draft 6-month plan of training cycles might look like this:
MONTHS 1-2 STRENGTH
MONTHS 2-3 ENDURANCE 1
MONTHS 4-5 SPEED
MONTHS 5-6 ENDURANCE 2
Linking Cycles
At the end of each cycle, you add a short rest period (about 4 days), which can include active rest, such as very gentle, long jogs, walks or swimming. You do this by slightly shortening the final week of the cycle. The next cycle then starts again with the same pattern, but focusing on a different activity or quality.
Understand that in all training, gains come at least 2 weeks after you have made them. That is how long it takes for your body to develop. So if you have just been training hard for 6 weeks, you could sit on your ass for the next two weeks and still perform better than today the next week (obviously, two weeks after that, you might drop off again though). This is why athletes take long active rest periods before important races.
Planning a cycle
Lets say your cycle is 6 weeks. Break that into individual weeks, following the graph above.
Week 1 - High quantity, Low quality (Medium load)
Week 2 - Low quantity, low quality (Low load)
Week 3 - Low quantity, medium quality (Low load)
Week 4 - Medium quantity, Medium quality (Medium load)
Week 4 - Medium quantity, High quality (Medium load)
Week 6 - High quantity, High quality (High load)
What varies, and can often be confusing, is defining quality. Quantity is fairly easy to define - reps, time spent, distance. Quality is more difficult. I usually read quality as "whatever I would be doing in the real event". Note that for most of the cycle, you aren't doing these kinds of session. It's only really the last week (which remember, is shorter to allow for a rest period) when you are consistently doing your hardest sessions. Also note: most sports do this differently, they add at least one high quality session a week. The example I'm using here is for endurance sports or competitions where you have to perform over a long period, sometimes several days. I'm using that because that is what matches most closely with P-Coy, which is 2 weeks of high performance. Ultimately, how you decide what is quality is down to you. The important part is to keep it consistent.
A training focus doesn't mean you only do that activity - for a strength focus, you don't just lift weights. But developing strength is the purpose of that focus, and everything else is a secondary activity. You prioritise the focus. So your main sessions in any given week will be weights, and your secondary and active rest sessions will be speed or endurance. This is what eliminates the tendency to plateau - during a Strength focus, you may feel like you aren't doing enough running, but that means you are "running rested" for the speed or endurance focus that comes next. You will see from my full example below that much of the activity you do isn't necessarily the focus activity. This is what cross-training means, and is also a contributor to the 80/20 rule (because a lot of the 80 isn't your race sport).
Weekly session pattern
Exactly how you plan your weekly sessions varies a lot, depending on what you are training for. When I've been at full training capacity for military fitness, it's 2-3 sessions a day, 5 days a week. That is a maximum. If you are just starting, do half that. Also, look at the example below, and you will see that most of those 2-3 sessions are really low rent - they should be enjoyable. For example, in the Strength section of the example, a lot of what I was doing was gentle sculling (single rowing) in the middle of summer. That's a pretty unchallenging, enjoyable activity, more sports tanning than training. It was a form of active rest and technical development. It had no direct relation to my training purpose (endurance fell running), but complemented my focus (as an upper body activity).
For P-Coy or endurance sports, I've found a 5-day on, 2-day rest pattern works best. This is simply because you are preparing your body for 5 days on. For single race events, a training/rest split of 3/1/2/1 is often used. Never skimp on the rest days. HOWEVER, a useful trick is to do active rest on one of your rest days. For your active rest session, do an activity from your next upcoming cycle. So in my example, during my Strength cycle, my active rest was long, slow jogs, in preparation for the Endurance running cycle next. This ensures you don't overtax your focus activity, but also maintain your overall fitness and prevent decline.
Pre-race period
If you are training for a race in 6 months, you also add a pre-race period. This should be at least 1 week, but can be as much as 2 weeks (see the point about gains above). During the pre-race period you conduct active rest. This means: flexibility, stretching, and long, slow versions of your race activity. One of the best uses of this period is to explore race routes. If you're doing a fell race, walk the route, perhaps with some light jogging.
Remember the rule of active rest is that you should never be working hard - if you are, even if you feel fine, slow it down. You need to be as disciplined about your rest sessions as you are about your maximum effort sessions.
1/2