Personal training has gone through fad after fad after fad. The current fad seems to be "muscle confusion" wherein the workouts are different every single time so your "body never adapts" to the workout! Can you believe that? Who DOESNT want their body to adapt to the work they are doing? If you are doing something different every time you step into the gym, you do not provide your body a consistent enough stimulus in which to get better. This is not to say that people do not see results from Crossfit, Insanity, Boot Camps or whatever other programs are out there, because people most definitely do. But the biggest results people see are psychological ("that was the hardest workout ever!"), and in a business that is based almost entirely on physique, lets do things that are effective and sustainable.
The first time you do an exercise, your body learns the motor patterns required to do it. The body is essentially establishing connections in which you learn the exact body position of that exercise. Now that your body is beginning to establish those connections, lets hammer them down over and over until the body says "alright, this isn't working anymore"! Teach your clients how to perform an exercise, such as a Goblet squat, then perform that exercise once to twice a week, every week until you stop seeing results! You wouldn't study for a math test by studying different history then math then biology then math then chemistry etc, so lets not apply that same philosophy to the weight room!
The key, though, is not to simply perform the exercise, but you must change some variable every time you perform it. An increase in volume (total number of reps) or intensity (weight of the exercise), or both if the client can handle it, are a must for continued results. Much like Jim Wendlers 5-3-1 Program, it has been shown that people can respond to the same exercise for months or years on end, simply with variations in volume and intensity. So lets apply that same principle to our clients and show them consistent results! If you do the same exercise with your client for 6 weeks, and go back and show them how much more weight they can move, you will have established yourself as their trainer. You are the guy who got them visible, tangible results.
The next question, you might wonder, is "will clients get bored with doing the same things every time?!" Yes, of course they will. It will get stale if you dont change something. So lets keep our core lifts the same, a squat, a push and a pull. Do not change these until you see a plateau for an extended period. But accessory work? Change it every 2-3 weeks (same principle applies, give the body a few sessions to adapt to the movement and get better, change when adaptation begins to slow or stops) to make sure that not only are you not neglecting a certain part of the body, you are keeping it fresh and interesting for the client.
Disagree? Agree? Please, discuss!