We launch a boat from our motor home every time out. Here are my thoughts. Teach someone how to drive the boat off and on the trailer. When you set up your boat to launch, put that person in the boat (they can pick up others after parking or drive directly to your site). When you approach the ramp if it is wide enough and not crowded, drive forward and make the u-turn as close to the water as possible so you don't have as far to back. If you can't see your boat when it is directly behind you in your mirrors, watch both mirrors as you back so that you will know immediately whether to make a correction. When backing in I usually back in far enough that the motor is all the way in the water, but most of the weight of the boat is still on the trailer, then once the wife has the boat started, I back up a little more and stop quick, and the boat pretty much launches itself.
Figure out how far into the water you need to be to retrieve the boat so that it will not quite float all the way to the winch, but will be resting on the bunks or rollers lightly to keep it straight. Once you figure out about where that is, find a landmark on the trailer (or paint one) where it enters the water. We use a couple of cheap walky-talkies and my wife (in the boat) tells me when I'm back far enough. The walky-talkies are also handy for launching and for coorinating when you are going to use the ramp in busy times. In the winter, I usually back down close enough to the dock that I can get on the trailer toungue to winch the boat the rest of the way, but during summer I usually wade. We've been using this system for years and once the same two people do it the same way it becomes second nature, pretty quick and no stress.
You said 1st time so: Unplug trailer lights, release tie downs, release winch line, Install drain plug, Lower outdrive, or outboard (only if clearance permits)(If not, wait until you get it in the water) I saw someone not raise their outdrive once when trailering their boat and drug it in the asphalt all the way up to the top of a very long ramp....not a pretty sight.
Don't get flustered....just take your time and you'll get used to it. Have fun.... 8) 8)