Firstly position your vehicle and trailer as straight as you can and roughly a trailer's length from the place you want to reverse. Keep your eyes on the trailer out of the driver's window while slowly reversing, and start turning the steering wheel towards the right. Grasp the wheel at the bottom and steer gently and progressively - it is fat easier to add more steering than to correct it after turning too much. Grasping the wheel at the bottom should prevent you from over-turning the wheel and if your steering wheel starts straight, you will know throughout the turn, without looking, that at the lowest point your wheels are straight again.
When the trailer starts to turn, start straightening up while still reversing. Leave straightening up too late and moving the wheel to quickly will cause the trailer to jack-knife.
Eventually you will be steering in the opposite direction whilst still reversing. Bring the vehicle's front around to follow the trailer and watch where the trailer is in case it needs to be corrected.
Continue reversing in a straight line looking in both mirrors. Reverse carefully and slowly. When you can see more of the trailer in one mirror, steer towards that side to start moving the trailer the other way. Corrections only require a small steering movement.
Moving forward to straighten the trailer is a simple option before continuing to reverse.
With practice you will be confident in your ability to back up several hundred feet without jack-knifing your trailer or rear-ending anything you are ready to launch your boat at a boat ramp. Try and select a quiet weekday morning for your first launch and have experienced help at hand...
This information is from the American boating association and I would recommend reading their complete article on boating
