practice - there is no magic formula. I am afraid you will have to sweat. Your coach should be able to "fine tune" technique
Formula I think I just found the formula on a piece of paper I have here. It says Milk, Eggs, Carrots, Cereal, Chips, Apples... Hey this is all stuff that I eat regularly, I'll bet my jab is really good! Jeese I'm out of most of those things tho, I should really write them down somewhere so I remember to buy them next time I'm at the store...
practise as much as possible, keep ur hand loose don't clench your fist untill the moment of impact. snap it
The power of your jab comes from your rear leg, explode forward with it and snap your hand it will improve.
You could use the method of when your keeping your hands up then when you throw the jab then snap it back in and it's almost like chambering but it's not with your legs but it's sorta like when you jab then you bring it back to your cheeks and maybe this would be a better way to improve jabbing.
ALL HAIL THE HYPNOTOAD! Other than that, low rep high weight resistance training. See the other recent jab thread. Also, distance is the key, make sure your target is right at the end of your snap.