With props, I usually give them a light grey primer first, paint the yellow a bit further than you need to along the blade, then mask the yellow to where you want it and paint something dark (gunship grey or intermediate blue) on the blades and then hit them with a few washes or dry brushings of black, leaving the leading edge of the blade in the grey for something of a worn look.
As for the wheels, take a strip of masking tape, larger than the diameter of the wheel hub and lay it over the wheel. once its tacked down good, take your #11 blade and gently cut the tape, using the underlying wheel rim as your knife guide, until you've cut all around. Now you have a mask for the center of the wheel while you're painting the tire and a mask for the tire while you're working on the wheel itself. Whichever part of the mask you aren't using can be stuck to a piece of foil wrapping or wax paper to keep it sticky.