Sand the rust off the wrench using medium-grit sandpaper. Depending on the severity of the rust, heavy-grit sandpaper might be needed. Clean adjustable wrenches by folding the sandpaper and placing the sandpaper into the grooves of the wrench. Wax the wrench after you have removed the rust.
Fill a large pail with sand and used motor oil, and set the pail along the side of the garage. Tie a small rope through the hole in the handle of the wrench. Push the wrench into the sand, and let it soak while the oil cleans and coats the wrench. Remove the wrench after a few hours, and wipe it off with a clean rag.
Make a paste of table salt and lemon juice. Smear the paste over the rusted parts of the wrench, and rub the paste into the rust. Remove the rust with a cloth.
Spray WD-40 onto the rusted areas of the wrench, and let the spray set on the wrench for 5 or 10 minutes. Wipe away the rust with a cloth. Remove stubborn rust spots with steel wool.
Spread Naval Jelly on the rusted parts of the wrench. Wait 60 minutes while the rust loosens, and wipe clean with a cloth. For stubborn rust, try another application and a bit of sandpaper.