Well here's my process, I sail solo and step the mast probably 80% of my outings:
1-The boat should be on the trailer and the truck/trailer pointing downhill (this is a must for safer and easier stepping).
2-Leave the boat tie down straps attached to keep the boat secured to the trailer. Remember, sailors sail in wind. A windy day and a raised mast without a secure boat could mean problems for you and anyone around you.
3-Remove and gently lay the head of the mast on the ground with the mast base near the cup. It (the base) will actually be a couple feet above the cup as the top of the mast rests on the ground. Have a rolled up towel on the center of the rear crossbar to cushion the mast. You can slide the mast back and forth as necessary later.
4-Attach your shrouds and trapeze wires to the mast tang first and lengthen and straighten them out to attach to the hulls. Then attach them to the hulls. I leave the trapeze wires wrapped around the shrouds at this point to prevent them from blowing around (I don't use bungy cord on the trapeze wires). Remember to have everything set properly with the correct shrouds on the right sides when you raise the mast. Also make sure the shrouds/wires are resting over the corners of the tramp. If not, they will become trapped under the corners when you begin the stepping process and you will become very ticked if you have to lower it back down to undo them. This can be done after step 5 but just make sure it gets done.
5-From atop the tramp, push down on the mast base and line up the mast base with the step link. Insert the pin and slowly release the pressure. The mast will be placing weight on the rear crossbar but the top should also be above the ground. This also causes the step to move upward.
6-Place the forestay with the pin in it under one of the tramp straps so you can get at it from atop the tramp after you raise the mast. Make sure the front bridle wire (attached to both hull fronts) is ready to go. It should be hanging down with the hole stay adjuster open (no pins on top).
7-Now comes the hard part. Raise the mast. From atop the tramp, since you've been up there anyway putting the step pin in place, walk back toward the rear of the tramp. While facing aft, reach down and pick up the mast as far back (toward the top of the mast) as you can while still on the tramp. Using your legs initially, begin to raise the mast. The reason you should be facing aft at this point is to confirm the shrouds are clear of the tramp frame. It will be heavy at first but the higher you go the lighter it gets. Also, if you followed step 1, as you go past the center point there will be little effort in placing the mast base in the cup. The step pin may be too high as you get to vertical. This is where you have to either (a)pull/jerk back on the mast base to get it set or (b) yell for a hand in pushing the base backwards so it sets. Once in, rest for a second. Hard part is over. But remember to keep the pressure on the mast forward so it doesn't come back down. That really sucks, and it rips mast bases and step pins out of masts and crossbars. :-( Another consideration here is the condition of your trampoline. If it is not in good condition you may want to place a sheet of wood over it to prevent yourself from puncturing thru it while you raise the mast. I would hope this isn't the case but don't want you to get hurt doing it.
8-My boat has a mast trailering/support bar just forward of the forward crossbar. It raises above the tramp about 2 feet. As the mast is leaning slightly forward (everything is downhill remember) and its weight is supported by the shrouds, I tie the bottom of the mast to the support bar with a 3 foot section of rope. Snug it up.
9-The next step is attaching the forestay. You should still be on the tramp and can reach down and pick it up out of the strapping material sewn onto the trampoline. If the strapping material is gone then tie a small piece of rope around the mast near the base and hook it to the rope during step 4 above. The mast should be resting against the support bar and the weight of the mast should be slightly forward. Check to see if that is the case. If not something is wrong. That shouldn't be the case if you've gotten this far. If so, slowly climb off the tramp and pull the forestay with you to attach to the bridle. Initially, use the top hole.
10-Slowly drive down to the launch area/beach where you will be setting everything else up. Remember that with the mast attached the center of gravity goes way up and too much lean could cause a problem.
11-Remove the boat from the trailer and place it facing into the wind on the beach/shoreline. Your rudders should have already been attached. Attach and raise the main first leaving the boom free, initially (kinda depends on the wind), then attach and raise the jib. Make sure your tiller is attached. Secure the jib to the jib sheet and the boom to the main sheet and traveler bar.
12-Secure your safety and required equipment to the boat. Check your work and head out for a safe sail. Good luck. Hope we've all helped a little anyway.