dynamic stretching, lots of passive stretching (ie. get the splits in spite of what other people says it helps alot.), practice lots of high kicks, and lift weights. im 5'6 and can hit 6'4 people in the head with round kicks. im so used to kicking high that when i fight someone my own size i actually kick over their head sometimes, but since im soo used to kicking reallly high kicking someone my own height in the head i can generate just as much power as when i throw a body kick.