First, remove all the surface rust. Just plain oiling won't get it. You will have remove the barreled/action from the stock to do the following. To remove the surface rust, take some fine brass wool (extra fine steel wool will work also), apply lots oil to the wool, and gently card or rub the entire outer surface of the receiver, barrel, and floorplate/trigger guard. Pay a little extra attention to the rust spots with the brass wool. If you use steel wool, be careful not to rub to hard, as you may remove the blueing.

After you have removed all the surface rust, apply a good quality oil. Before the hunting season, you may want to apply something like Birchwoood-Casey's SHEATH. It comes in a can to be wiped on or in areasol to be sprayed on. It will dry to create a film over the metal surface, that will not "acciddentally" wipe off or wash off in the rain. Also Brownell's LTS-1 areasol works great to.