well, i used to just throw and catch the double but it always was very hit n miss like you said. basically from there i tried the bar catch bar and that is pretty easy. you just need a fair bit of air time for it. all you really need to do is be able to commit to a really late second barry. try doing it on the ground, just bar catch bar. once you have the motion fairly well in your head, just go straight up and do it. that learns u to know when to grab the second barspin. once i did that, i moved on to bar flick bar where i dont even touch the second hand, i just give it an extra flick around with my hand. i found it really easy to do it like that cause u can flick it really fast around. like, i can do it with a foot air out of a 4ft quater. some people like that way, others stick to catching in between. but yeah, basically once you have that then you know when to catch and straight double bars become heaps easier.
hope it helped
