Well first off try to start on a big trampoline of some sort. If you get enough air you don't even have to tuck that much and that way you can get used to the motion of leaning back.
Also get a rhythm down, like when I back tuck I always jump, lean back, slap my knees (the tucking part) and then untuck. This is of course done very fast and the slap on my knees makes a nice clap sound when I am exactly mid-air (a very nice novelty). By using this rhythm technique I can always rely on muscle memory and take a fairly complicated trick and turn it into something a kindergarten kid can do. I realize that my backflips are actually better then my front flips because of this, I sometimes over tuck or un tuck to soon on my flips because its really a guess for me when to un tuck.
generally once you know how to do a backflip it is much easier then any other kind of flip because its total muscle memory.
