Move the boat to the end of the dock or if possible, to the opposite side of the dock away from the boat ramp. Remove the winch strap or cable from the bow eye and the safety chain and push the boat into the water while your crew holds dock lines attached to both bow and stern. Once you've reached the water level where the boat can be launched, put the vehicle in park, set the parking brake, and chock the front wheels if you wish for extra security. It's easier than making huge swings to correct. If the trailer starts to jackknife or becomes difficult to straighten, go forward just enough to straighten out and start again. When your hand moves left or right, the trailer will go in the same direction. When backing the boat trailer, put your hand on the bottom of the steering wheel.
Roll down the windows in the tow vehicle so you can communicate with your help and have everyone else get out of the vehicle before you back down the ramp. This may also be the time to partially lower the outboard or stern drive but don't let it bottom out on the way down the ramp.
Install the drain plug and remove the transom saver if you use one. Disconnect tie-downs and transom straps but keep the boat attached to the trailer with both the winch bow strap and the safety chain on the bow eye. If you have a starting battery switch turn it on now and insert the ignition key. Move coolers and as much other gear from the tow vehicle to the boat.