Good advice from all these guys. The fish tape is especially essential if you're running down an exterior wall with insulation. If not, many times you can get away with a piece of string and a fishing weight tied to the end.

As far as patching drywall goes, here's a very simple way: If it's not already, square up the hole by trimming the edges. Cut a square patch exactly two inches larger than your hole in both directions. Score the patch on one side one inch from the edge on all edges. Then carefully break the drywall along the scores and peel the edges off the paper on the other side. You should now be left with a patch the size of your hole and one inch of paper extending in each direction. Put some drywall mud on the edges of your hole and press the patch in the hole. Use a drywall knife to squeeze out any excess mud by dragging it over the edges of the patch. Then use drywall mud on the outside of the patch to cover the edges of the paper. Sand and paint.

Pictures of this method found here under heading "Patching Small Holes in Wallboard"