Improving my kick and punching

Anybody can tell me what exercises can i do to improve my punching and kick strength?

Hit the heavy bag, hit the heavy bag, and hit the heavy bag!

oh yeah, thanks NotRoy

pardon my stupidity but which heavy bag?, boxing heavy bag? or the thai heavy bag?(you know the long skinny one), is there a difference between either of those 2 as far as kicking speed or conditioning of shins?, thank you

Power involves speed as well, so hitting the bag TOO much can be counterproductive. Many times people end up "pushing" the bag with their strikes rather than keeping their punches and kicks crisp and snappy.

Hit the heavy bag--BUT...

Add plyometric drills. Jumping squats and clap pushups are a good place to start.

STRETCH! Speed plays a big role in how hard you hit, and speed comes from (among other things) being relaxed. Stretching helps with this, and also makes it easier to keep good form. I spend a lot of time stretching my hips, back, and shoulders.

Double end bag work will also increase your speed and timing.

As far a what type of bag, I have never seen a "Thai bag" in Thailand. Kick whatever you have access to.