Dead hang pullovers require proficiency and strength in pike lifts and pullups. (A pike lift is when you hold onto an overhead bar and perform a leg raise with knees locked and toes pointed - touch toes, feet, or shins to the bar, and reverse, all in a slow cadence.) A potential training progression towards a dead hang pullover from a high bar -
Australian pullups on a low bar - build up to 2 sets of 20 at a slow cadence with proper form; a partner can give you a light spot under your shoulders; good partner cues are "squeeze my fingers with your shoulder blades", "try to pull the bar down into the floor", and "stay hollow" (the last one reminds him or her to keep the toes pointed and midsection tensed).
Partner assisted pullups on a high bar - build up to 2 sets of 10 at a slow cadence with proper form; partner can give a light spot through your legs at first, and once you can do 10 this way, have your partner give you a light spot by placing his or her palm in the center of your upper back (just below the shoulder blades), and pushing just enough to get you through the concentric sticking point
Self assisted pullups - you can use a few different self assisted methods. One way is to use varying degrees of leg assistance. The easiest variation is to get directly under a bar that is at a height that will allow you to keep a hold of it while still standing on the contact surface (mat or floor, for example) and at least slightly bending at the knee. Basically, you are starting at a dead hang while at least partially squatting down. Assist the upwards pulling motion by standing up straight, but do so with a slow cadence. As your chin clears the bar, tuck your feet behind you and hold the topmost position for a 1 second count, then place your feet back onto the contact surface and slowly lower back down into the bottom position.
To make this harder, simply place your feet a little further out so that your legs will not be able to help as much. This takes some experimentation. Build up to performing jackknife pullups, where your legs are fully straightened out and at about a 90 degree angle to the torso. Place a mat or block under the feet if needed, or ask for partner assistance. As you pull upwards, you can still press down slightly through the heels. You will want to be "hollowed out" with the legs when you get to the top position.
Pullups without assistance - build up to 2 sets of 10 at a slow cadence with proper form; keep the body in hollow and the midsection tight; drill scapular retraction and hollow body drills separately if needed to ingrain proper technique and full body tension.
L-hang pullups - build up to 2 sets of 10 at a slow cadence with proper form.
Self assisted pullover - there are a few ways to self assist. They all deal with generating momentum for the pullover. I can cover these in a future article.
Dead hang pullover - get a hold of a high bar, start performing a pullup, and as you are pulling your torso up to the bar, start lifting your legs up to the bar. It will look like a mixture of a pullup and a pike lift. Your goal is to pull your waist to the bar. From there, roll your hips over the bar, then roll your wrists up to the top of the bar and lock out into jump front support position.
Dead hang pullovers are easier if you can grip the bar without having to jump to reach it.