My training system has grown fairly complex over the past few years. Its based on some simple principals, so i'm hoping to bring things back to basics a bit over the next while.
I have the following core principals.
1) train for what you want to be.
Are you wanting to be a powerlifter? A dancer? A distance runner? Are you after the body of one of these in particular? Surprise! The best way to either be one or look like one is to train like one!
Strength and Endurance are fairly self explanitory. If your training all for strength, you get little endurance. If its all endurance, you'll find it hard to build strength. The human body can only do so much.
You will notice that there is an overlap area, while not having the same maximum capacity as all strength or endurance, it has an overall higher capacity when you consider them both as seperate values (I prepared a graph, but for the life of me cant figure out how to upload a plain image without it needing to allready be online.). This is because I beleive there is a certain synergy that occures when one trains for both goals. No you will never be as strong as the those training all strength, and you will run out of gas befor those who are all endurance, but you will be overall better off. This however comes at a price. your training needs to include meathods from both strength and endurance training, and can be much more difficult to do properly. This is the road i like to try and travel.
2) Dont waste effort.
Ever see the guy doing endless bicep curls at the gym? That guy stands there for 45 minutes, to make sure his biceps maintain thier 18". All the while his legs are dispropotionate, and due to the fact every exercise he does his core is being supported, he has no means of actually using all that power.
You are allways better to do compound exercises. Ones that hit all the muscles possible. Pushups, pullups, squats, the plank, bridges... these all use many muscle groups. The result is instead of training one muscle for 45 minutes, you train your whole body. No you wont have 18" arms... But you'll have a highly functional body capable of taking on real world tasks.
3) Train for reality
Are you ever going to need to squat 600lbs? How about bench 350? When in the modern world will you need to be able to run 26 miles in 2 hours 40 minutes? These are stupid goals.
Much better to train for what actually happens. You might need to move 5km in a short period of time. it happens. your at the park, and you realize you forgot to go to the store, but your bus leaves in 30 minutes. so you run. You could need to pour a 100lb sack of concrete into a mixer to do a renovation. Train for goals that are within reason and need, and you'll have far more time to cover more goals.
4) Eat properly
Without a proper diet, covering all your bases you will never reach any of your goals. If you are feeling sore for an abnormal amount of time after a workout, your lacking one of the building blocks nessicary for muscle growth (theres more to it than just protein). Are you tired? When was the last time you got more than 3 servings of fruit and veg in a day, let alone the 10 you should be eating. Do you need two hands to count the times you've been to a fast food place in the last month?
We are what we eat, and nutrition plays the largest role in what your body is able to do. Pay attention to it and educate yourself as much as possible.
5) Obay the laws of physics
When you think about what you want to be able to do, look to Newtons laws for guidance. Think about how your body has to move to perform 'x'. What forces are at play? Where does this force go? Are you unable to do the task? If so, can you figure out where the weak link is?
6) Train as often as you need to
Some people train every day. Some train 5 days a week. Others train 3. Some do 2 leg days, 2 upper body days. Others do 6 jumping jacks, 2 cardio days, 1.623459 NOT 1.623549 upper body days per week.. All this is stupid. Train as much as you need to to meet your goals. If you obay law 4 and law 2, you wont over train. You'll have the resorces you need to make progress, and every workout will be a full body one. If you can meet your goals off of 2 10 minute sessions of burpees per week, fly at it. If you need an hour a day every day, well good for you. Dont get caught up in how you SHOULD train, and concentrate on how you ARE training. Does it work for you? Will it meet your goals?
How you train is up to you. Its my opinion that you should allways train with certain goals in mind, and try to devise the best way to get there.