You can't develop both at once. Start with accuracy drills, of which there are a number in the 'Finishing and Passing' subforum of the Featured Articles section with only maybe 30-50% power. After you can reliably hit the corners, or a given spot, then is time to work up power.
Power won't come from leg muscle strength, or swinging your leg any harder or any of this, it's really down to proper form. That is, a superbly locked ankle that strikes the ball instep first about its middle. You will leap off your plant foot quite naturally as you hit the ball to give it some extra power. As well, to keep it low and strong, as well as to promote good balance, your hips will have to be square to the ball, and over it. Your plant foot will need to be firm and relatively close to the ball when you hit it.
First step to having a more accurate and more powerful shot is to put less effort in.
When you apply a lot of effort into a strike, your leg muscles are all contracting. This is not good because it makes your leg a rigid lever with no flexibility, therefore you cannot generate good leg speed and your chance of injury is dramatically increased. Think, if your muscles can only deliver a set amount of force, you only want the ones generating forward force to be contracting when striking, if you are tense and other muscles are creating a backwards force, then the overall force applied to the ball will be less.
There is also the issue with accuracy, no matter how good you are, a tense body and leg will never strike the ball cleanly. Everything should be relaxed smooth and controlled. When you hit flawless shots with an almost arrogant smooth swing form, then you start to increase your power by decreasing execution time.
what klc said worked for me, yesterday i went out to practice shooting and my shots were faster but the most noticble differnce was accuracy, the ball was going where i wanted most of the time
Some other tips I suggest is to practice good technique. Make sure to have the ankle locked.
Have your non kicking foot not to far from the ball and pointing in the direction of the target. Keep head down and body over the ball.
Landing on kicking foot can also help generate power.
Of course you have to practice your shooting often. Also having strong legs will help as well.