I tend to play the ball forward and parallel my shoulders with the slope on downhill lies to try and get the ball up higher in the air. When I play it back I tend to hit it heavy due to the shortened distance from the top of my swing to the ball compared to a flat lie. On an uphill lie, it depends on the wind. If it is helping, I play it up in the stance to so as to get the ball as high as possible so the wind has a chance to push it further. If the wind is in my face, i take an extra club or two and play it back of my stance like a knock down and try to keep it under the wind. Another trick is to take an extra club and hit a high fade if you can control it if there is relatively no wind.