Not really relevant, but not moving feet.
Most mistakes with the jab is trying to make it a power punch, or being square on.
Always remember the jab is a set-up punch it is neither heavier punch or leaves you off-balance.
Do not forget a feint is as good as a punch, so no need to punch all the time. Less action is better.
My best jab involve moving my front foot and I expend very little energy, I am never off balance and ready to throw a straight right, or if advanced a left hook off the jab as long as you move the front foot outside the opponents lead leg.
Common mistakes are trying to throw a fast punch, when you can throw a powerful punch.
Always trying to do double, triple jabs with the last punch being the most powerful, if you can not throw a triple jab without being off-balance or the last punch being powerful you are not boxing and need more practice.
Best advice is the jab is not a knock out punch so do not treat it as such