Ollie north, never been able to do them. At 30 years old and on the board for 16, I can say I've landed probably like 5. My friends do them with ease, while I'm over here sweating bullets trying.
think of it as a kickflip without the ankle flick. you ollie then kick straight off the nose, really like you would for a good kickflip but you don't use your ankle, you keep your foot stiff and solid. back foot on the board controls it by keeping it flat, to prevent flippage but really like it would for a normal ollie so you don't think about it.
Mark Renton's problem on 360 flips has to be upper body-related. if you land in front of the board, you're leaning forwards too much. upper body should be straight, perpendicular to the ground - don't bend like you're looking over your nose, sit on that back leg instead. you pop and scoop with the big toe on your back foot, over the edge. shoulders facing where you're going and you never move them or the board will fly out of control. really try using the pop too so they don't look too flat or varial kickflippish. then don't turn your hips either and aim for the bolts (sounds dumb but for this trick it really works). if you keep landing in front of the nose, try leaning back more. if (like me) you're not a natural at that trick then yes it can get frustrating, but it's really worth it when you get it down. I know I've always refused to learn it without the pop, like most kids do them (which seems to enable them to do them super easily, but personally I've never liked that look, I kind of like the struggle on those).