So many people come in complaining that they slept wrong that I wanted to address the topic. For back sleepers you should have a low pillow that fits nicely into the crook of your neck without pushing you head to far up. As well as a pillow under the knees to take pressure off the knee joint. For side sleepers there is a lot more to it. You want a pillow that allows your spine to be completely horizontal to your bed without your shoulder being rolled in. The pillow should cradle your head and support the crook of your neck. There should also be a pillow between the legs to prevent unneeded pressure on the hip joint. This will take some time for you to adapt to a higher pillow for side sleepers but your body will thank you.