step up from a prostaff 550

the optics and range finder are fine. I would like to know what would be the next step to a compact 1200 or so rangefinder.
Also, what is the best method for streadying (sp?) while range finding. I have to lean against a tree or my car while holding my elbows in close

Go for the cream of the crop, the Leica CRF Rangemaster 1200. This is ridiculously bright compared to other rangefinders, and it's one of the smallest. You are steadying your rangefinder correctly. Besides a walking stick or a bipod, there's nothing else you can do.