While the need to `run-in` a car has diminished with man-made technology, the same cannot be said of the raw materials involved in cricket bat manufacturing. The knocking in process is ideally completed in five stages. The weakest part of the blade is the edge and knocking in should concentrate on this area.
1/ Using an old ball or preferably a bat mallet, starting gently, strike the bat to mimic a ball deflecting off the edge of the bat.
2/ Increase the impact and continue until the edges have visible rounded.
3/ Again with an old ball or mallet, work gently on the face of the blade.
4/ Use the bat in a net session against older balls.
5/ Finally, increase the hardness of the ball, perhaps with some throw-downs.