If you've ever painted anything before, then you probably know that you're supposed to make sure the painted surface is clean before you get started. However, just how do you make sure the surface is clean enough before you start painting? Well, you could wipe it down with vinegar for one. Just use a bit of vinegar to wipe down your wall, or whatever else it is you have to paint, and it should strip all of the dirt and grime away.
Of course, make sure everything is completely dry before you start painting; otherwise, you risk having some moisture trapped underneath the paint, which might have to be sanded down and repainted later.