Beyond the usual? Work your way 360° around the heavy bag popping them nonstop, circling first clockwise and then counterclockwise and then changing your distance from the bag, to and fro, until you can throw a short inside jab moving left with roughly equal comfort as throwing a long one at "proper" jabbing range moving right. Use the double-end bag to improve accuracy landing on a moving target. Fire a moderately heavy straight right hand to set the bag on a less predictable course than if you just gave yourself a cupcake tee-ball start with a jab, and try keeping the points of contact as near textbook form as you can (first knuckles of the middle and index finger square on the bag dead-center) Work the mitts with somebody who really knows what they're doing and can push and challenge you with different wrinkles (forcing you on the backfoot, making you duck or slip punches and counter with the jab, etc) If you have a gym with a bunch of bags suspended from the ceiling in rows, do full perimeter runs, snapping the pivot at each corner, and jab every bag you pass. As that becomes easier, double jab, and triple, and so forth. Ladder exercise. Pop two left jabs before a right cross on the heavy bag. Then 4, then 6, then 8, 10 and 12 and then back down until 2. Switch to southpaw, repeat. Shadowbox. A lot. I mean that's all super basic, elementary stuff - but those are how you drill the jab. :conf Not sure what exactly you were looking for, or what about the jab you're looking to improve...hence the fairly general (and probably not all that helpful) answer.
Stand against the wall, with your jab shoulder against it. Plus elbow and fist also touching. Then throw a jab and keep repeating, at all times the shoulder and elbow and fist never leaving the wall. Fist finishing palm down, great way of learning the mechanics.
Throw a lot of jabs. Hang a towel or jacket on something and pop/snap it with your jab. Work a double end bag with the jab only. Do a jab 1-10-1 jab pyramid every day. Jab people you know at random. Jab people you don't know at random.
:good Pyramid/ladder exercises are great ways to simulate in-fight conditions, both in terms of acclimating to firing lots of jabs but also keeping your arms up (something a lot of boxers struggle with even at high levels in the pros) without fatiguing. :rofl
If you want to have a good jab, this may be the most valuable instruction you will ever receive. Learn to keep your elbow down.
Try weighted shadow boxing! But slowly at first with perferct form, if you can jab with a dumbbell like a mad man it'll be effortless in the ring. I know the Durable Dane did A lot of weighted shadowboxing and he had the workrate of a pedigree work horse just some unspoken advice. Another less relevant odd tip is standing in your stance motionless with moderately heavy dumbbells to keep you from fatiguing out of your defensive position remember to keep those hands up! "Bring the jab back quicker then you throw it"
I am also interested in this question and I saw a lot of lessons on YouTube how to make powerful punch, and they all are about you should make your body muscles more strong. On some forum I saw a video where Conor Mac Gregor trains with x1 training tool to make his punch more powerful. I opened a new theme on this forum and I am wondering is it possible to increase your punch power as it was written by manufacturers due to stabilization muscles
