Clean off the blade. Using an old cloth, rub on the sides of the blade, removing any loose particles. Take steel wool and rub at the rust-covered areas, removing as much of the rust as you can without applying too much pressure. If there is little rust present, you can just get the blades sharpened to remove it.
Roll a lemon either between your hands or on a counter, but apply pressure so you're squeezing the lemon. Cut the lemon in half and squeeze one half onto a cloth. If half of the lemon doesn't cover the whole cloth, then you can use the second half.
Use the cloth you soaked in lemon juice and rub down the blade, making sure you're covering all the rust in lemon. Let the lemon juice sit on the blades for a minute then wipe it off with a clean cloth.
Use steel wool to wipe at any rust left after you wipe the lemon juice off. Don't apply too much pressure with the steel wool or you may scrape away too much of the blade.