Piston Break-in?

Ride it easy 15 minutes....cool down 15 minutes......ride easy again 15 minutes.......cool down again 15 minutes.................ride with varying throttle levels another 30 minutes...........cool down again.........ride a little more aggressive but never wide open or real high rpm 45-1 hour.................cool down completely again. Take it easy that first day. The cool down is as important as the warming up.

Just to add to what Braahp said.

After the initial break-in you should check and retorque the head and cylinder bolts then give it an oil change (if its a 4stroke).