When making a side hill putt, either left to right or right to left, tilt toward the hill. For example, if you are making a right to left putt your eyes will naturally set up outside the target line causing you to putt toward the inside of the hole. Conversely, if you are making a left to right putt your eyes will naturally set up inside the target line and cause you to putt toward the outside edge of the hole. To counter both of these tendencies simply tilt your body toward the hill. This will put your eyes over the target line and give you an accurate perspective of the target line toward the hole.