If your bike has a continuous cable housing re-cableing is ultra easy. Simply replace the cable and the housing one-at-a-time and use the housing to guide the cable and the cable to guide the housing.

If you have a bare wire running through your frame tube, figure out how to position your bike so that the cable exit is pointing straight down. Feed the cable through the frame while you watch the exit. Gravity will guide the cable to where you can snag it with a bent piece of wire or something.