I use the "break it in hard" method. My engines allways run great, and have very little blow-by.
First... I fire it up to make sure things are pumping, and running properly with no leaks. (For a ski... do this in the water, but still on the trailer)
Next... get it up to temp... and open the throttle for about 5 to 10 seconds... followed by a long closed throttle deceleration. This creates high vacuum in the engine, and forces the rings to seat completely. Do this 3 or 4 times, and head back to shore to check over the engine.
If everything is good, and no adjustments need to be done... just go out and ride the ski like normal. after the initial full throttle blasts... you want to NOT hold the throttle in any one position for very long. (keep changing RPM's)
Oh... you will also want to run the first 2 tanks of fuel with a little extra oil. I recommend 2 oz/gal. (in a boat, one tank is fine)