I think a big thing is to remember to work on both your strengths and weaknesses. Sometimes people get so caught up in fixing a bad backhand, that their forehand, which was a relative strength, is neutralized because they don't work on it. Unless you're amazing everywhere, it's good to have a shot that people fear a little bit. It forces their hand.
Another thing is to really strategize, not just hit the ball. Say someone has a weak forehand volley. How can you exploit that?
I've always found that my best tools are my variety and my movement. Sometimes you'll run across people who just can't handle a low skidding slice to their forehand. If you can make them hit that, you'll be golden even if they are the superior player in every other facet. I'm a two-hander but there have been matches where I've literally only hit backhand slices because it made my opponent uncomfortable.
Also, don't undervalue lobs or other defensive shots. While it's true that Roger Federer will put that overhead away 99% of the time, easy put aways are missed A LOT at the club level. Don't feel like you have to hit a brilliant passing shot down the line just because you are moved off the court. You're not a professional.
When going for your shots, margin is your friend. I've heard a lot of people give the 3x3 rule, meaning your shots should land three feet away from any lines. I don't necessarily subcribe to that, but really you don't need to be looking to hit clean winners unless the person is just a great defender. A lot of times making someone hit a forehand on the run is enough to get either a very weak reply or an error.
Obviously, the higher up you go, the less margin you can afford, and the better your defensive shots have to be, but remember that your opponents are amateurs just as you are.
Great advice...my backhand had always been my strength, but for a few years I've been trying to add power/accuracy to my serve and forehand. It hurt my backhand a bit, but then I slowed down a bit a few days ago and concentrated on the wrist snap, and it seems back to normal. I never want to hit a backhand as badly as I had the last few times before that though.