I found this neat video over at golftipsmag.com. PGA teaching pro Jeff Johnson left this video with a very simple tip to improve your shots from a sidehill lie.
This is really simple, folks; it's all about posture. While this lie requires you to bend your knees a bit more -- so you can get down closer to the ball -- you have to make sure that you don't "sit back" into the hill too much. If you do, you'll end up swinging too flat, too much along the line of the slope, and that will make it hard to get the ball up in the air. If you don't get it up in the air, you aren't going to hit it very far!
On the other hand, you don't have to lean toward the ball so much that you lose your balance. Just make sure that you lean forward enough to get an upright swing. That's how you dig down and make solid contact with the ball.
Don't forget that the ball is going to curve down along the side of the slope. (That's a slice, no matter whether you're a leftie or a rightie. They included a trace of the ball's flight near the end of the video. See how much it curved?) You'll probably need to aim more uphill so the ball doesn't curve into even worse trouble.