Hanspeter made a good lesson discussion practice. I'm sure this will add to what Kevin just suggested.
http://www.guitartricks.com/lesson.php?input=9745
When I work on a specific exercise and I'm able to play perfectly, I move on to another for the few days. After a couple of practice session without practicing that exercise I go back to it and see how I'm doing. Sometimes your able to nail it right away, sometimes you realize you have to work on it a bit more. Going back and forth like that using 2-3 key exercises (like the 3 notes per string Kevin suggest) will help you burn them into your mind.
There are some things I used to play when I started playing guitar that I can still recall 16 years later. Usually it's because I've practiced them on and off over the years.
