I presume you have studied this:
http://www.youtube.com/watch?v=wB75gG3ugUU
I did and screwed it up royally the first dozen times, then realized a few simple simple tricks. I put it on and off the trailer by myself all the time now.
If you have a trailer that has bunks, don't try to blast the boat up onto it. With the rear wheel of your truck just in or at the water, the forward bunks should be just under water (drop the tailgate so you can see this). Better to be a little deep. Slowly nestle the boat onto the trailer, letting the forward bunks line your bow up. Then STEER the boat as you push it up the trailer, keeping it aligned with the bunks by using your rudder. You can even stick your head out of the window next to the helm to see what your alignment is over the fenders on your trailer. Don't be afraid to use a lot of power, but be sure to back off as you get close to the trailer stop.
Once you have "doinked" the stop, climb out on the dock and check your alignment. If the stop is not centered on the bow stem, it is easy to push or pull the rails near the stern to line the boat up. Even a boat hook works. Remember, the stern is still floating. Then climb into your truck bed, step off the tailgate onto the trailer, attach the strap and snug the boat up to the stop.
Then haul it out knowing full well that there will be about six inches between the stop and the bow stem when the boat settles onto the trailer. I usually set my hydraulic brake controller on its highest level, cruise across the parking lot at about 15 mph and slam on the brakes. That usually snugs it back up so I can finish tightening the strap.
Then I climb back Into the boat to discover that full, open beer I had left out on the table has now emptied itself in the cabin along with anything else I had not secured for a collision. It only took one of those to learn the lesson, tho.
As was noted previously, nothing beats practice, which I view as an excuse to go boating.
The launching and retrieving drama is gone, and I am much relieved.