steering wheel.
3rd tip: find that trailer tire in your driver's mirror (or passenger as the case might be), and using tip #2, keep it aligned with where you want it to go. In the case of a boat ramp, keep it aligned (with some clearance) to the edge.
Misc. Tip: don't drop that wheel off the boat ramp edge, especially if you've only got 2WD. A wet boat ramp, 2WD, and a trailer axel now bottomed out on the boat ramp is a great way to have a ton of time to figure out your next move while everyone else is staring and fuming at the idiot now stuck on the boat ramp.