Karate is a form of martial arts in which people who have had years and years of training can, using only their hands and feet, make some of the worst movies in the history of the world.
Chagatai's Rules of Martial Arts Movies, Version 1.0 :
1. Watch some good Kung Fu flicks from Hong Kong. This includes many movies starring Jet Li, such as Fist of Legend (very little wirework), Fong Sai Yuk (partial comedy), Last Hero In China (comedy with lots of wirework), and Tai Chi Master (best plot I have seen in a Kung Fu flick; one of my favorites). Take notes. Watch the camera angles and speed.
2. Learn martial arts. The worst thing you can see is someone who doesn't know a roundhouse kick from a side thrust trying to look stylish and professional. And I don't mean just enroll in your local "Karate Shack's One Free Month of Lessons With Uniform" deal. Find a good school and stick with it for several months. It will help make you look good both in form and physically, which brings me to point #3...
3. Few people have the "Kung Fu" look. This is quite simple. There are few people in life who look like models. There are also few people in life who look like badass martial artists. Chances are if you are a 6'2" white guy with a gut, even if you can kick over your head and do backflips, it won't look good. You need people in your movie who can intimidate, have a defined musculature, and can do all of the moves.
Costumes and makeup can also help.
But, don't get me wrong, there are roles for people who might not be in the best of shape. For instance, a "round" fellow can look like a good Tai Chi master and play the part convincingly.
4. Choreography. The trick here is to go imbetween looking totally scripted and not scripted enough. You want all of your characters to have power in their moves, finesse, and skill that is exhibited. But you also don't want it to look like a scripted, "I punch here, you block there," type of thing. The moves need to be fluid and slightly eccentric, and continually shifting camera angles make all of the difference.
5. Plot. Research the history and period of what kind of a flick that you want to make. You don't want to see a Kung Fu flick where the main guy has a samurai sword. By the same token, a karate fighter should not try Capeoria moves. Make everything authentic. And there are certain plots that you must avoid, namely anything that has "ninjas" or "street fighting" in it. These are waaaaay overdone.
6. Kitsch. To finish up your movie, find some trait that stands out. Maybe you have a "one-armed swordsman," maybe you have an erratic weapon like in the movie "Master of the Flying Guillotine," maybe you have someone who can summon inner power and shoot concussive force out of their hands. Find something that sets apart your movie from the rest.
Good luck.
(Footnote: Chagatai is a 6' 10" white guy with long red hair who has been studying Kung Fu since he was 16, and is now nearing 23. He knows his role in any Kung Fu flick would be the big dumb guy or the strong, "smash you into the ceiling" type guy. Feel free to e-mail him at logiq@holly.colostate.edu)