an_ders, here's a quick run down of how I solo launch and retrieve without a dock (I plan on doing some of these videos in the spring).
Overall prep away from ramp (everything ready and unhooked except for winch strap). Back in boat. Climb in boat, unhook, back off trailer. Beach the boat and climb off (depending on where you are, your feet might get wet). Usually I'll tie up to a tree near shore just to be safe. Park my truck, get back in the boat, and start fishing!
Retrieve (pretty much the opposite):
Beach the boat and tie to a tree. Back in the trailer. Load the boat (I prefer to power load, but most launches without a dock will likely be less developed so you might have to crank it instead - I take it on a ramp by ramp basis to make sure I'm not ruining everything (both on my boat and on the ramp). Make sure winch and safety sharp are secure. Pull the boat out of the way and finish securing it for the drive home wishing I had more time to fish.
I have a bunk trailer... Roller trailers might be a slightly different process but the concept is basically the same.
Regarding the power loading thing, since I know people get passionate about it... There's a big difference between a launch that usually has a dock (usually concrete pretty far back) and a place that never has a dock and might just be gravel and sand. You can power load on the developed ones and not ruin anything, just don't hammer down on the throttle and you can do it without creating potholes. You'll likely still have to crank a little remaining slack. Don't bother trying to power load with shallow or just gravel ramps. You'll ding your prop and ruin the ramp for everybody else. The rule of thumb I use is the shorter the distance of concrete underwater, the less power I use and the more I end up cranking. Try to picture where your prop wash would be in relation to the ramp and where other trailer's tires might be. Trim the motor up to prevent scraping and keep possible prop wash upward instead of straight to the bottom. I've used that concept for years and I've never left the ramp in any worse shape than I found it.