Originally Posted by Onganju

Repitition is definitely key. If you want a good reference guide for MMA Striking, I would find Mark Hatmaker's "Savage Strikes." It is a good introductory guide for striking in MMA. It breaks down the Kinesthetics of punching pretty well, and it addressed elbow, knees and kicks too. This should be a good start, as you noted you're primarily a grappler. If you were an advanced striker, I wouldn't recommend it as readily. But at $10, there isn't too much to lose.

The reason why I noted getting a reference book first, is that you can get a an idea of the finer movements that have to go into the punch. From there, if you don't have anyone with boxing knowledge/experience, you can train technique with a better idea of what to correct. The first requirement for power in strikes is speed/acceleration. The second would be mass.

Remember: Force = Mass * Acceleration. If your able to get your arms moving at a decent speed, then you have to train the rest of your body to move along with it to lend mass to your punches. I could go on in length on it, but I think you get the point.