well, hopefully you do enough research to get your own answer and don't listen to people who go against the (sand) grain... vacuuming your sand bed is not a good idea. why would you suck up your substrate? if you have enough of a clean up crew, if you have enough flow, and don't overfeed, your sand should be clean.
the only thing i'd suggest is to vacuum the rock a tad, but be warned you will suck up pods. pods are beneficial detrivores you don't want to throw out. you're better off taking a turkey baster and blowing all the stuff off the rocks, then suck up the waste as it is suspended in your water column.
also, remember water changes aren't just to remove old water, it is to replenish trace elements you don't realize you're system is using up. that's why the 2 week water change rule is suggested