I see two mistakes made alot when superman diving which often result in people hitting knees first.
Mistake 1. Slowing down your run just before you dive, if anything speed up ! commit to it, if you bottle it just before you do it then you won't slide very far and you won't have enough speed, commit go for it, and make sure your upper body is kind of falling forward and you are almost stumbling for the last part a fraction of a second before you push off into the dive.
Mistake 2. Not kicking your legs up to ensure you slightly land chest/forearms first
kick your legs up and back towards your buttocks, it doesn't need to be a massive kick but the aim is to help you to land slightly chest and forearms first, which is what you want to do for a sucessful superman dive, watch the pro's, especially ollie lang, if you look at him mid dive his knees/legs are slightly higher up in the air than his forearms/chest, if you don't kick pretty much right after you push off it is highly likely you will hit the ground knees first which will result in either a very slow slide or no slide at all which is not very helpful !
This video has a good angle which kind of demonstrates the point I am trying to make about your landing being chest/forearms first
Notice how he does not slow down at all before he dives, he speeds up and pushes off into it, and his landing is pretty much textbook perfect.
This is how not to superman dive, no push off, did not kick his legs, and slowed down just before he went down, and it was pretty much just a fall onto his front from which he had to crawl.....
