How can you do the kick where you extend and contrsct the legs straight? It always gos to the side by me, even if I tilt my back and stuff...

Hmm, this isnt rapid thread discusion, I belive.

/ontopic Try to use the lumbar and the chest :>

Extend the foot that you are extending the leg on.

Moved to a more appropriate place. (BS)

relax the knee =D

No one can help you the way you can help yourself.

My only tip would be:
Experiment with all your joints, everytime you practice you get better till a point that you'll be able to create your own moves.

Hope this helped.
good luck.

If the problem is: when you are trying to kick you end up moving away from uke rather then towards him/it.

Try relaxing the knee that is pushing you back. Ex. If your moving you right leg forward, your foot is contacting the ground, thus you'll move backwards. If you relax the knee on this leg, it will move the leg forward without moving you backwards.

If this isn't the answer you were looking for, feel free to pm me.