Don't know if the obvious has been mentioned but, if there is one close to you, regular pump track or bmx track practice will really help. It won't be much fun at first but stick with it and your pump/manual/jump skills should improve. You don't really need a specific bike either (although a proper DH bike won't be much use) - just run your summer tyres with 40psi +.
I grew up riding bmx before switching to mtb in my 20's. However I found that after having kids, and reaching about 40 (I'm 43 now), I shy away from bigger jumps, particularly doubles.