OK.
So you are running. You should be running leaning forward somewhat, if a dive is in your future. Your hand, if you reach for the ground, should be about as low as your knee, maybe lower if you reached straight down, but don't reach straight down, leave it a bit in front of you. The way I like to land is to sort of push forward with one foot, as if continuing to run, but instead of putting the other foot forward, try to just keep both legs sort of together. That will make your upper body get closer to the ground very fast. My empty hand hits the ground first, then my gun arm hits next, while sort of curling my wrist so that the barrel is pointed up (cuz dirt in barrels is no good). So my empty hand and my gun forearm are on the ground, like sled runners of justice. Then I basically roll my body onto the ground, belly to hips to thighs.
As for getting over the mental block, go buy a Slip 'n' Slide and practice diving onto it. It says weight limit 60 lbs on the box, but screw that, this is a training device, and it must be destroyed. In fact, once you have destroyed it, you will find your self diving on grass (unless you set it up on a gravel lot like I did). This might make your ribs/ abs sore. I have no pity for your eensy little tum-tum, though. You will eventually get stronger (and more scraped up).
The key is to have more forward momentum, and no upward momentum. If you bounce up when you push into your slide, you will stop short and you will hurt. Then you will get shot. Then everyone will talk about what a terrible slide that was. Horizontal, not vertical, this is your mantra.