I had a great conversation today with a friend and the topic of perceived exertion came up. I hope everyone has had a chance to read some of the content I wrote the last few weeks on basic resistance exercise. The first step is to follow a resistance training program that is practical and effective. See the following link.
The second step is to train progressively. This means that over time you must either increase the number of repetitions per set with a given load or increase the load. During the initial weeks of commencing a resistance training routine, your focus is to establish a baseline of resistance and repetitions per set. After a few resistance training sessions, you must begin pushing yourself on each set. Each set should be taken to or very close to volitional fatigue. Meaning that you complete the maximum number of repetitions you can per set. Of course, this advice is for an orthopedically sound individual that has no underlying injuries.
For an advanced trainee, you may want to stop a set 1-2 repetitions short of failure. I would take more days of recovery if progression does not occur or if you find you cannot exert maximal effort. Ensuring optimal recovery is one reason I suggest resistance training just one or two days per week. Resistance exercise is a high-intensity exercise where progression is the foundation.