Thre things are key for me for these, first keep my shoulders parallel to the slope. Never fight the slope by going against it. Second never try for a full swing if the slope is fairly severe. It's just too easy to lose a bit of balance and get off plane. Third always take a good practice swing and see where I am brushing the ground and then move my body so that the brush will align with where the ball is, never try to change where you are brushing the ground so you can hit the ball, it just ain't natural. Not sure if any of those will help you but they do me!

 

 I think the first comment in keeping your shoulders parallel to the slope of the ground is key to the success in these type of shots.  IMHO, Good Luck!

The steps that i take are this... I play the ball back in my stance. I aim slighly left of the target. I make my normal swing, making sure that i swing down the hill. For a side hill lie... I play the ball toward the toe(when above my feet) and toward the heel when below my feet. Aim slightly left Keep my knees bent(especially when the ball is below my feet Make my normal swing. I have since gotten better at these since i have stopped my over the top tendecies. I played a course called Castle Rock in Giles County VA, i have never seen a course that undulates as much as this course...every hole was a dog leg, 3 of the par threes could not be seen from the tee box... Man was it fun and a great place to master down hill and side hill lies. Shot a 73 +2 over par... Putter was on fire...I love those days....