start on something smaller and just learn how to get into it at the right height (not hopping over or kissing the end). once you learn how to get into it and your weight is in the right place youre just learning how to keep your balance like with a regular boardslide, etc. alll practice
but learning how to get into it in the right spot (what youre having trouble with) is the key. you could learn going 1 mph and just jumping on in the right place, then eventually speed up. most grinds I learned were the opposite (alll speed) but for this it helps to learn how to get into it the right way since your back is turned and its not really natural.
wrote a book now saying the same thing over and over but hope that helps!