INCREASING THE INTENSITY
There are actually two ways to do this:
Personally, I use the first method, as it allows me to more accurately guage my progress. With this method, you find a rep target, (like 8 for my Chest), and strive to reach that target with every workout. Rather than increasing the number of reps however, you increase the weight. Now here is the key point: You only increase the weight by miniscule amounts at a time! I increase my weight by only 1lbs. a week!
The trouble with the way most people train, is that they are doing fine with 170 lbs. for 10 reps with the Bench Press, so the next week they increase it by 10 lbs., and barely eke out the required 10 reps. The week after they increase by 5 lbs. and do only 8 reps(They are still kind of happy because they increased the weight). The week after that, they remain at 8 reps with no weight increase, or worse, injure themselves b y using sloppy form to complete the sets. Since they suddenly are not progressing, they get discouraged, and either make an excuse not to go back to the gym, or try to find another exercise (like Incline Presses) that they can respond to.
What I am trying to say, is that everybody needs to experience some progress to stay fired up about working out. EVERYBODY! People make the mistake of biting off more than they can chew, and end up failing sooner or later... But..if you only add 1lb. a week, I'm sure that you will be able to complete the required reps! It may not seem like much of an accomplishment, but think of it this way, in one year, that's a 52 lbs. increase in the amount you can Bench. When was the last time that you had that kind of increase (besides when you first started out, as your muscles were getting used to it), after a year of doing it the old way?
To summarize, the key points for this type of working out are as follows:
On a personal note, when I first started doing Squats, I used 160 lbs. for two sets of twenty reps. In the second set, I was exhausted, and it took a lot of bullet biting (and inward cursing) to finish out those last 5 reps. I wrote down in my log book "Second set of Squats, last five reps were killer, felt like passing out, almost vomited" The next week however, I was able to do that second set easily. Though I didn't increase the reps, or the weight, I knew by reading my log book that I had improved, and I was raring to go !!