If you execute your workouts using the same rep ranges, you will get minimal results. The strategy... For weight lifters with at least 1 month of weight lifting experience:
For a whole week, workout using heavier weights (with strict form), 6 to 8 reps per set.
Then, for a whole week, move onto a workout session where you are using 10 to 12 reps per set in every workout.
Then, for a whole week, use a rep range where you are using 15 for your rep range.
As you can see, the reps are changing, so obviously the weight you are using is changing too. You are going from reasonably heavy weight (without over doing it), then begin challenging yourself on a weekly basis, by exhausting the muscles further using lighter weight.
Does this mean light weight means less muscle? No.
Does this mean heavy weight means more muscle? No.
Does this mean that if we offer the muscles both heavy, moderate, and light weight workouts, that we ultimately work more muscle fibers, causing more of a growth response? Bingo!
It means you are targeting more muscle fibers by executing your weight training differently each time.
Variety of rep ranges will target more muscle fibers and thus a growth response.
Here's the best workout with this style of training: Weight Training Routine For MASS
So whether you are using heavy weight and doing less reps, or if you are doing light weight with more reps, the key is to change it up.
If you've only been working out for less than a month, stick with full body workouts first, done 3 times a week, before attempting the method above.
So a strategy for someone just beginning, would look something like this:
Pick one exercise for every muscle. Do about 2 or 3 sets per exercise. Approximately 10 to 15 reps per set.
Example: (This is for beginners only)
You will be targeting legs, back, chest, arms, shoulders, and abs, every other day, with these exercises:
Flat bench press
Do this 3 times a week for about a month.
After a month of this kind of training, move on to the methods we discussed above, which is:
1 week of heavy training
1 week of moderate training
1 week of light weight training
In this 3 week period, you will be using 3 or 4 exercises per muscle group, and you may workout 2 muscle groups per workout.