Concave...whats the secret??

In preparation for shaping my new board, I was thinking that I would try putting a little concave in the nose. Whats the secret, if any, to doing this properly? For a 9’2" board, whats the best size for concave and in what proximity to center should I put it to center? I appreciate everyones help!!!

Try searching the archive, its been dicussed quite a few times.