Ball Above Your Feet
You'll have a tendency to pull the ball down the slope so aim to the right of your target. Shorten the club by choking down the grip and stand slightly more upright with a little less knee relex.
The result of this is that you should feel that you are swinging the club around your body in a slightly more rounded swing plane. Rotate your body through to a finish and maintain your balance.
Ball Below Your Feet
The key to this shot is to maintain your original height as much as possible. If you try to stand too tall over the ball, the result may be a topped or thin ball.
Grip the club towards the top of the shaft. The ball will tend to fly right, so aim left of the target. To get yourself down to the level of the ball, bend from the hips more than you would do normally, widen your stance for stability and flex your knees. Due to your inhibited turn you won't generate as much power so club up accordingly. Try and swing as freely as possible within the confines of the slope.
Ball On An Upslope
Because the launch angle is high, you can take more club, for example, a 7-iron instead of an 8-iron. Once you have selected the right club, check your posture. Your right shoulder will be lower than your left and your weight favouring the back foot. Adopt a slightly wider stance than normal and aim to the right of the target as the ball will have a tendency to hook from an upslope. Keep your weight stable and your head down through impact and let the natural momentum of your swing pull you into the finish position.
Ball On A Downslope
This is the toughest shot of all. The nature of the downslope means you are deprived of loft and it is all too easy to scuttle the ball back into the ground.
To combat the downslope, take less club than normal, for example, a 6-iron instead of a 5-iron. Make sure that your shoulders and hips are parallel to the slope. Pace the ball back in your stance, and pick the club up a little steeper in you backswing with early wrist hinge. This will allow you to generate a steep angle of attack. As you swing down, try to feel as though you are chasing the ball down the slope. The golden rule here is to resist the urge to scoop the ball into the air.