Then, I cut up the individual letters on the second set and put them in a pile with the roll of tape. Then I had my son pick any letter and he had to match it underneath the one already on the wall. While he did that we went over certain things that start with the particular letter.
My son doesn't have much of an attention span so we did about five letters at a time and then went back for more later. Easy, simple and they learn a little something along the way.