u need a really strong core - 'inner unit' and 'outer unit'. this is where all you torque and power originates from. get on a swiss ball, BOSU and/or air disc
get a strength base by performing compound movements such as bench press, leg press (moving on to squats after a month or so), shoulder press, chin ups and barbell row. then add some plyometrics, such as depth jumps.
also up hill sprints are good.
Olympic lifts are arguably the most effective, but u need someone to instruct u.
this is a useful site :
http://www.dolfzine.com/page2.htm
u also need to replicate the movements u need power for, e.g. a punch, using a cable machine, and or medicine ball.
in addition, when u perform weight lifting movements, perform them at speed. e.g. bench press with lighter weight, but push it up as quick as poss, bring it down controlled, then explode upwards again. do not lock out ur elbows. this is v good with a med ball and a partner.
complex training is also good. perform one set of bench press followed by 1 set of explosive chest passes with a med ball