Many elements add together to make a good stroke. Many elements executed very well add up to an accurate, powerful stroke.
First of all, relax. If you are too tight, and "forcing" your actions- that will limit your power.
Find the right "balance point" with your weight moving forward so that you hit the ball right at the point where, without some correction, you would, otherwise, tip forward- and that is when you should drive through the ball.
Many people are confused about adding topspin to the ball and try to "brush up", but forget to drive through the ball. If you are using lots of effort and the ball is going nowhere fast- this could be your problem. Forget "brushing". Think, instead of driving through the ball from low to high.
Keep a fairly loose wrist, and do not try to impose any "wrist action" on the ball. Keep your swing simple and unforced. Practice the motion without a ball until it seems fluid.
Make sure you get to the ball early and get set up in position so all your strokes are, basically the same- and you are not "improvising" or inventing new stroks or positions as you go.
Practice your shots at a comfortable, medium, pace- then when you finally get the rhythm down, increase the speed, but keep everything else the same.
And, as someone mentioned above- practice. Get yourself to a wall or a ball machine and refine your stroke through dozens/hundreds of repitions until it all comes smoothly and effortlessly. The key isrefinement, smoothness, looseness, not force.