The most important of which is, you have to be able to see the trailer. This might mean putting extended mirrors on the tow car. These are available at automotive stores and can have either permanent or temporary mountings. For very low trailers you may want to add a couple of bright fiberglass poles so you can see it when the boat isn't on it. These can be available from bicycle stores for a few dollars each.
More people get into trouble trying to rush than for any other reason.
Place both hands at the bottom of the wheel and move them in the direction you want the rear of the trailer to go. With this method, it doesn't matter if you're looking out the back window or in the mirrors. Take your rig to an empty parking lot and practice backing it into different areas. The two-wheel trailers do have a tendency to turn very sharply once they start, so back them even more carefully. Above all, don't be reluctant to pull forward and start over if a backing operation is going badly.