One easy trick is to make a guide from a wire coat hanger. Simply twist one end of the coat hanger around the lip of the coupler on the trailer, taking several wraps, so that the coat hanger stands perpendicular to the trailer tongue. Tie a small piece of cloth to the upper tip of the wire for better visibility. Now, when you back up, all you have to do is center that wire on your tow vehicle and you know the ball and the coupler are in close proximity. If you drive an SUV, you can make things even easier by bending the upper tip of the wire forward, so that it will just touch the back glass of your truck when the ball and coupler are perfectly aligned. Once you're lined up, remove the wire and you're ready to go. You can also fashion a guide out of a flexible bicycle flag. Attach it to the coupler and you're set.