With a B-Twist all it is is doing your b-kick but corking at the height of your jump. Are you trying to spin facing forward when you're taking off? If you are stop that right now. Bad things happen. Trust me. Bad things happen.
For a higher jump all it is is more arm and leg. That's all you can do. One thing about tricking is you can't halfass anything or you mess up. You really have to be throwing yourself into the stuff. Do you start with a b-kick in place or do you do your b-kick with the little run up and the spin thing. The spin is what I do and it gives you a lot more power because your hands are already swinging.
When I do my b-twists I do the little run and spin start and dip down super super lower with my arms completely outstretched. When that first arm gets passed my front leg I jump as hard as I can with as much force as possible. I try to make the jump hard enough that when you land you won't want to trick for like 10 minutes because you put so much energy into that one trick. So really jump with that front leg. Then when I get in the air I keep my arms completely straight out until the highest point of the kick then I snap my arms in really quick and throw a super fast cork. If you do it like this you should have plenty of height and then it's all about just landing right.
They say you only really need to know how to do a b-kick to move onto b-twists but I also had to learn corkscrews before I could do b-twists. Just keep trying man. They took me 4 months before I landed my first one.
Here's the tutorial I used if this didn't answer your questions.
http://www.youtube.com/watch?v=918ze-gxKJQ
