In general, you'll be better off with your right foot pointed forward, as opposed to pointing to the side, as you are in the video. You only wanted pointed that way for a left hook.
When you jab you are shifting weight on your feet, onto your left foot, which you do not want to do. Any hip turn on a jab is very very minimal and your front foot should not pivot when you jab. Also, shoot that arm all the way out, fully extend it. Part way is an open door for eating right hands. As to clenching your hands, an exercise for jabbing that has worked well with me is "catching flies." Shoot your jab and snatch them out of the air.
Your right hand is all in one motion. It should be sequential: Weight goes to the left foot, right toe pivots to turn the right hip, which turns the right shoulder, which drives the right arm, which propels the fist. It is a whiplash effect from the ground up. You can feel it, doing it slowly, culminating in the explosiveness of the punch. The left hook works the same way, as do the uppercuts.