Move your weight back, relax your arms, feather the back brake, dont touch the front, drop the seat post, dare yourself to stay off the brakes, accept falling off is a possibility, wear armour.
Example, me on red route at Glentress, forgot all of above, hit ramp and got airborne, locked wheels, smashed into ground, went home in ambulance with broken collar bone ! Once healed started with little hills, did all of the stuff in my advice, built up to steeper hills and now do red route at Glentress with ease.
Practice, knowledge, precautions and knowing ultimately its the bestest fun on two wheels keep making me do it. Push yourself a little at a time and eventually you'll get there !