The 3 to 5 method became popular through the writings of Pavel Tsatsouline. (Pavel has to be, by the way, one of the most innovative writers out there when it comes to building strength, power and muscle mass; and, oh yeah, he's also the guy who singlehandedly made kettlebells popular in the states.) Pavel's method - if I'm correct - meant performing 3 to 5 exercises for 3 to 5 sets of 3 to 5 reps. You then trained every 3 to 5 days.
Mine was/is a little different. Pick 3 to 5 "core" exercises. These should be the "more bang for your buck" movements. You want to pick one squatting exercise, one "pulling" exercise, one exercise for your upper body "push" muscles, one exercise for your upper body "pull" muscles, and (if you so choose) one other exercise for either your arms or your ab muscles. If you are feeling at all drained or overtrained, you can drop one or two of the above exercises and just perform 3 exercises instead of 5.
On each exercise, perform 3 to 5 sets for 3 to 5 reps.
Train - and here's the difference with my system - 3 to 5 days each week. For myself, when training in this manner I enjoy working out Monday-Friday, then taking the weekends off. Sure, I feel a little overworked and tired by Friday, but after taking Saturday and Sunday off, I feel refreshed and invigorated for Monday's session.
Obviously, in each workout, you need to leave a little something "in the tank." Stop each set a few reps shy of muscular failure. And don't get "jacked up" or over energized for any of the workouts. Relax during the workouts; taking a couple of minutes of rest between each set, and practice some deep, meditative breathing between each set, as well.
Here is an example of what a week of training might look like:
Monday, Wednesday, Friday
Squats: 5 sets of 3 reps
Deadlifts off Blocks: 3 sets of 3 reps
Incline Bench Presses: 3 sets of 5 reps
Chins: 5 sets of 5 reps
Barbell Curls: 3 sets of 3 reps
Tuesday and Thursday
Front Squats: 3 sets of 5 reps
Flat Dumbbell Bench Presses: 3 sets of 3 reps
Bent Over Rows: 5 sets of 3 reps
Steep Incline Sit Ups (weighted): 5 sets of 5 reps
When first training in this manner, you might want to ease into your workouts the first week. Also, you should feel refreshed and energized after each workout; probably a lot better than when you started the session. And don't be upset if your strength is up and down throughout the program. Some days, you will feel a little more tired than on others. On these days, make sure you are still performing 3 to 5 sets of 3 to 5 reps on each exercise you choose—don't shortcut yourself. On other days, you will feel very strong—resist the urge to do more on these days and just stick with the program.