A few rules when you are at the ramp:

1. Preparation
Do all the preparations in the parking area away from the ramp. If you are new to the ramp check it out before you launch. Park your car away from the ramp and walk to it to check the depth of the water and slippery areas.
It is important not to gear near the ramp until your boat - and you for this matter - is ready to launch. Nothing shortens tempers like someone who drives to the ramp and then proceeds to undo straps, prepare the boat when all the others are waiting
2. You have prepared your boat, what is next?

2. Launching your boat

- While the driver reverses down the ramp, someone else walks beside the vehicle holding the painter (bow line) prepared to push-off the boat from the trailer.
- Move the boat to the dock
- To clear the ramp area, the person on foot can walk the boat around the offside of the dock.
- The driver parks the vehicle and trailer, and returns to the boat.
- If you have mechanical issues such as the engine won't start, either launch the boat and tie off to a dock, or leave the boat on the trailer and move to the side. One should never "work" on the boat while blocking the ramp to others.
- Most anglers launch in the predawn hours, backing a boat in the dark can be difficult for some in crowded situations. Do everyone a favor and turn off your headlamps while waiting in line, it could get YOU on the water faster if the guy ahead of you can see what he's doing.

3. Returning to the ramp

- When you return to the ramp, approach the ramp area and tie-off to the waiting dock, never tie off in the ramp area blocking others from using it.
- If possible drop-off a person to retrieve the vehicle and trailer. Back the boat away into the lake.
- Wait for your trailer to be positioned on the ramp.
- Once your boat is on the trailer, raise the propeller and immediately move the boat to the far end of the parking lot or out of the way of the ramp, only then should you proceed to remove plugs and gear and install straps. etc.

Extras
Launching and loading your boat should be routine, you should at least have a mental check list that you go over as you prepare to launch. By being prepared you'll avoid that last minute rush that inevitably leads to forgetting things, such as putting the plug in the boat!

And a clip that is showing all you have to do.

This is another piece of valuable information from this place and this really looks like a great guide comparing to others that could be found here. I really think that checking every single detail is the most important thing in completing and successfully getting your boat onto the trailer without much trouble, and most importantly, successful in getting it offshore. I believe that everyone wanted to see their boat going offshore without damage and most importantly, nobody gets hurt.