Follow the Mototune method..... Or just go out and do lots of starts and stops..... It's all about putting lots of pressure on the piston rings to make a complete seal before the cross hatching is worn off the cylinder walls. Idling around, or running at a constant speed is not what you want to do. Varying the throttle, or better yet, hard starts and stops, is what you want to do.
My dealer told me he's had boats come in that ran like absolute crap. The owners were paranoid about break-in, and literally idled around the lake for the first 10 hours. That tells you something right there..... Running it hard is better than babying it too much....