Get yourself a gravel cleaner siphon hose like those famous “Python’s†and clean out a little section of your sand bed on each water change. Don’t try to clean the entire sand bed in a single water change because this may disrupt the bio-filtration activities that are already established there.
I agree with Rob also, depending on what sand bed you are running will determine how deep you can vaccum. A deep sand bed, you don't want to disrupt the lower levels by vaccuming too deep, but with a shallow sand bed, you can go and should go, straight through to the bottom