A couple quick tips without getting into it too much.

1) Get yours off first, don't wait on your opponent.
2) Throw jabs in 2's, 3's,4's, not 1 at a time.
3) After you throw any combinations, jab your way out. Do not back out without putting something in their face.
4) Make sure u get it back after u throw it, do not get lazy with it.

There are many things to do/not do with the jab, these are a few that may help u out. Good luck.