When faced with an uphill or downhill lie, it is common for amateur golfers to either hit the ball fat or thin. The mishit is most often caused by an error in the setup position. so, focus on getting your set up correct.
It is supremely important that you make sure your shoulders are parallel to the ground on which you are hitting from and not parallel to the horizon. This is by far the most common way to misplay an uneven lie in golf. By setting up in with your shoulders parallel to the ground you're effectively mimicking a flat surface. If you don't believe me ask a fried to take a picture of you setting up. IF your shoulders are parallel to the ground you'll be able to rotate the picture and save it making it appear that you're actually on flat ground. If your shoulders are parallel to the horizon the rotate picture will look like you're either aiming at the ground or up into the sky. You'll know right away if your set up is correct or not.
By creating a the same relationship between your body, your swing and the ground as you do when you actually have a flat lie you'll find that the swing is the same and the mechanics are unchanged from what you've hopefully become accustomed.
Setting up with your shoulders parallel to the ground will allow the lowest point of the swinging club face to be achieved at (or in fact just below) the ball rather than before or after, and thus reduce the chance of hitting the ball fat or thin.