First of all, you should always unplug your computer before opening it up. This will help to avoid any potential damage that could be caused by water or other cleaning solutions coming into contact with live electrical components. If you're going to be using a vacuum cleaner, be sure to use one that has a soft brush attachment. You don't want to risk damaging delicate components inside your computer with a hard, metal vacuum nozzle. You should also avoid static electricity build-up by either touching a metal object before handling any sensitive components, or by wearing an anti-static wrist strap.