It usually depends on the bat, but commonly you just need a lot of good BP with the bat. You have to have between 100 to 200 hits to break it in. Some bats take longer than others. You need to be hitting goods balls, leather cover solid baseballs. Hitting off a tee will not break it in very effectively. You need to be hitting live balls thrown 40mph or better. A machine works good if it is set up to throw real baseballs. Each time you make good contact you need to turn the barrel about 1/8 turn so you break in the bat evenly.