I can do many of those kicks Bruce Lee can and its acheivable by ballistic streching. Before you do any workout go up to a wall and have both hands on the wall. Then start swinging you leg back and forth for about 10 -12 times each leg. Then after that form a karate front stance and swing you leg as high as you can and tuck your hips under your leg. Do this 10-12 times both legs. Those are two very rudimentry streches for high kicking. Then after you are done training or working out then do static streching. Static streching is your splits, chinese splits, hurdle strech hamstring and quadricep steches etc. etc. Static streching releives the lactic acid that forms in your body after a workout/training session anyway so its good to do. Its very simple you can just strech to do the high kicks, if you want to kick then simply kick as high as you can until you can kick higher and higher. Pretty soon you will develop more balance and coordination too. Good luck on becoming a better kicker and practitioner.