the 4front tech talk video helped me a lot. admittedly i've only done them into an airbag but I was landing them consistently doing it.
Go into the jump with your hands out in front, knees bent. Maybe hands a little lower than in front. As you approach the lip throw your hands up and behind you and look at them the whole way. The big part for me was taking my eyes off the landing in front of you. Think about it this way..for a 360 your landing isn't in front of you...you need to look around the other side of you to find it. Its the same with a backflip. The landing is somewhere behind your head but its really easy not to look for it and to just hope the flip will come. it wont. You need to look for it. What the guys above said about your hips is absolutely correct. Hips forward and head back with stiff abs will have you throwing them perfectly and spotting your landing from half way around.
The big thing is confidence. Once you realise how quickly the flip comes around its a really easy trick. That's when you can start experimenting with getting your hips out earlier and laying it out. To begin with, keep it simple. Hands up, head back, tuck the knees up when you're half way around to pull it around. Throwing it hard with your arms isnt the best technique but it WILL get you around and give you the confidence to start slowing down the whole thing.
Watch the 4front tech talk episode too. They show you how easy it really is.
Also have a look at my photos. There's a sequence shot of me doing a backie. It's not the best technique in the world but it breaks it down into components.
