i would like to train in a way that someone who would fight in a mma contest would. not just boxing, but all types of fighting. like what would i need to train for, size, strength, or endurance? what kind of exercises could i do that would help me hit harder and last longer in a fight?

you would need to periodize and cycle the training, power, speed then strength on 1-3 month cycles mixing sport specific work with some specific weight and conditioning work.  Plyometrics once per week are also great for this sport. 
I also suggest a good mix of arts like akido, muay thai, grappling work like sambo or jujitsu/judo, boxing/kickboxing for some stand up.

Come Visit my websites!
www.figureteam.com
www.lindacusmano.com
www.bodyrushpersonaltraining.com

If your not involved in a fighting sport then you should join 1 or 2 for a start. The most basic mix is boxing for stand up with wrestling for ground. On the lifting part is exactly what ~Italianangel~ said. You should just drop any isometric exercises you do, since the looks of muscle is not a factor to a fighter. Doing olympic lifts, compound, and pylometrics is types of lifting you should be doing. Maxing out your NM for your body will help you out in being stronger then others equal to your size.

We should live our lives as though Christ was coming this afternoon. - Jimmy Carter

Power comes from your legs.  Squat.