What is an efficient workout?

When is it not enough or when is it too much exercise? Because not everyone's muscle growth is the same, there is no concise answer. As a starter, meaning you probably have never been to a gym before, its good to do one or two different exercises for every muscle. Do this for about a three week period and your body will be ready to begin a real workout. Consider it the warm-up phase.
For those who have been lifting weights for a while but do not know what type of routine to stick with, there is the basic session that works for everybody. This workout consists of making active two muscle groups. A major group, for example your pectorals, and a minor like your triceps. Exercising muscles that complement each other make for a better, more productive, session.

Ideally, an hour well spent at the gym will have you do the following:

1. Warm-up your muscles
2. Exercise
3. Stretch

The portion you are actually lifting weights should look like this:

Muscle Group A

1. Exercise 1 (4 sets, 12 reps each)
2. Exercise 2 (4 sets, 12 reps each)
3. Exercise 3 (4 sets, 12 reps each)
4. Exercise 4 (4 sets, 12 reps each)

Muscle Group B

1. Exercise 1 (4 sets, 12 reps each)
2. Exercise 2 (4 sets, 12 reps each)
3. Exercise 3 (4 sets, 12 reps each)
4. Exercise 4 (4 sets, 12 reps each)

What makes each set different is how you increase the weight. It does not have to be a constant 5-10 lbs increment every time. What you want to do is do a set on a weight that will challenge you, but enables you to complete the 12 repetitions to the end.

If you are constant with such a routine, you'll start noticing those sexy differences in no time!