Hands in pullup grip (pronated), pull the chin over the bar, while also pulling the knees to the chest. This exercise can be done repetitively, or used as an isometric exercise where we hold the chin over the bar, and knees to the chest for a period of time.
Entering a pullover, do not drop the legs down, instead let them push out against the ropes. In this inverted “candle” position, press the ribcage down and tuck the tailbone under. Keeping the head in line with the spine pull the shoulder blades back and down as you pull your hips closer to the bar. Try to keep the elbows close together, not flaring out to the sides. At first the pull may not feel very large, but eventually your long term goal is to pull until the bar is at your navel.