Which type of diver did you get? Jet, Deep 6, Pink lady, Dipsy?
Are you running a flasher/dodger as well?
As a general rule consider your rod length. When your gear is reeled up you don't want the leader to be so long it makes landing the fish more difficult.
3' to a flasher, another 3' to 5' to your herring, or simply 5' from diver to baits.