Keep it simple
Here's one of my games from a while back. I was playing a much lower rated opponent, and by keeping things simple and playing logical chess, I was able to win convincingly by take advantage of his mistakes. It is worthwhile noticing that he was the one trying to force the issue by initiating exchanges, threatening attacks etc., until one neat tactic finishes it all:
A good example of how to approach a game against a much lower rated opponent - notice how I simply sat and waited for him to make the mistakes, while playing sensibly. Nevertheless, when the moment comes to attack, I did, and I had to, for otherwise the opportunity may not have come again.