I have had a few terrible personal trainers in the past and, in fact, those experiences made me very hesitant to try it again. However, I gave it another try, and I'm glad I did. This is why I like my current trainer:
1. He listens and observes. He knows what my goals are, and he knows what my strengths and weaknesses are.
2. He tailors. Based on number 1 above, he tailors my workouts. My workouts are "my" workouts--not some cookie-cutter program he uses with every client.
3. He is friendly but not overfamiliar. Sure, we have smalltalk and have built a rapport while we are working, but we don't waste training time becoming buddies. In other words, he respects my time as much as I respect his. When I pay for a 60 min session, I don't expect to only get 55 min of torture. Likewise, when he agrees to train me 60 min, he doesn't get just 55 min of my effort.
4. He is dependable. I fired my last trainer because he stood me up--one time was all it took. If either my current trainer or I have to cancel, it is well communicated and it is rare.
5. He knows about fitness. This should be a given, but it's not. There are many trainers, particularly younger ones, who know enough to regurgitate basics and to tell you what got them in great shape. I prefer a trainer who understands the human body, how muscles develop, how to incorporate rest into the routine, how to avoid injury, and how to recognize when an adjustment to the routine is needed.
6. He trains for total health. I see him three times a week, but we discuss my other training days when I'm on my own, my supplement usage, and my dietary progress. I can call him if I have a question--although I don't do that much.
7. He motivates. He doesn't indulge excuses. I don't offer any, but I've seen a few other clients who did, and he was pretty blunt with them--we all have to take ownership of our health and he makes that point clear. However, he does this without being a jerk about it. Tremendous knowledge with no interpersonal skills is of no value in a trainer (I've unfortunately seen that combination of attributes from a few of the posters on this site when some knowledge-seeker like me asks a question).
Sure, my trainer has his faults. At first he comes across as really arrogant, but he's not as bad as I originally thought. But I don't care, as long as he keeps doing the things listed above and I keep progressing toward my goals, I'll stick with him.