depends what type of bat it is?
i had a andian made bat it was the softest willow i have ever seen u cud push ur nail into it and it would dent so easy..
so i spent ages knocked it in with a mallet gentle hits made big marks so i just did it gently untill all the dents where now flat.. then just did it harder and harder etc untill i felt it would take a ball.
the key for soft indian bats is the edge make sure you round them off as they are usually left sharp and like 90 degrees. this makes the edges look alot bigger but trust me you dont want to take an edge with out rounding them off it will split and crack, i roughly spent 5 hours knocking in my indian one.. and then it impreved with a netting etc but now after 2 seasons i felt it was a little bit dead. if no longer felt like it was pinging off the bat and just felt like it was dead,.
so i purchased a solitaire 1st thing i notice was how the quality of the wood was so much better it had a much better colour and was properly a good 40% harder. i couldnt dent it with my finger nail and smashing the mallet on the bat didnt dent it . with this one i just went up and down the the whole blade for about 2 hours then used it in the nets and its an absolute monster!
so my knocking in experiance hasnt been grate and im probs doing it wrong but it works for me none of my bats have broke and they have been used well!
im a big hitter so get alot of edges and some of the back of the bat so far so good