I've been an exercise and wellness coach for about 18 years now. The biggest issue is I see is a lack of adaptation of people's training programs. Most people do the same thing for years. They see short-term gains, but fail to either maintain them or continue progressing.
Think of exercise as a skill. Like any skill, you have to progress from the basics first, then progressively overload and stimulate the body for continuous gains. This approach also prevents injury by making sure you that properly prepare the body for increasing demands.
I gathered 4 articles below by Tudor Bompa, who pioneered the idea of training periodization. These articles pretty much summarize what a periodized program would look like.
I would focus on the repetitions recommended for each phase of training. Repetitions are the most important variable for determining the intensity of your workout (assuming you're using a load that allows you to work within the repetition range so that you reach fatigue at the end).
Whatever exercises you select (that's up to you and your goals)...by applying a periodized approach, you'll get much better gains.
If you already know all this...then just disregard it.
Hope it helps. http://bit.ly/bompastrength