As stated guide on poles or side bunks are a must when doing a single man operation, I fish my 150 all the time alone and it all boils down to you developing a system for yourself that works for you.
What I do is I pull up to the boat preparation area and get everything ready, pull straps, motor support, place plugs, hoist antenna, make sure ropes are in place neatly coiled and ready to go, keys in boat, all gear aboard, got fishing license? And I try to do the entire operation in 1 to 2 circles around the boat.
Then I make one last trip around the boat and hit the primer bulb a few squeezes and launch.
My rig being fairly light I can push off the trailer when the rear of the middle bunks are barely under water. So I back down and I watch the tops of the fenders for the correct depth (I took a magic marker and drew a 3" long line I could see in the side mirror). I then get out and only then,
and only then unhook the safety chain and put the winch in reverse and slack off the winch strap and unhook.
I already have the 30' bow line in hand and all it takes is a firm push and we are on the water. I let the boat clear the trailer get on the dock and pull the boat out to where I tie it off and then go park the trailer.
Retrieval is just about as simple, put the trailer in the water to the mark, drive the boat on the trailer (Raise the motor a tad for safety's sake) I get with in 3-4 feet of the winch but yours will differ. Stop motor, raise motor, step over bow onto trailer or bunks, hook up and winch her up,
hook up the safety chain, lock the winch and get off the ramp so you don't hold up others.
I got some 2" 3M non skid tape to put on the top of the trailer rails where I step after I did a graceful splat on the ramp in about 10" of water this year when I slipped.
Of course there were lots of witnesses and one comment was "That ought to register a 2.8 on the Richter scale"
Non skid is good stuff.
Always hook up that safety chain on the trailer, I've seen winches fail and people leave a boat sitting on the ramp and no easy way to get it back on.