First set: c m a t
Second set: s r i p
Third set: b f o g
Fourth set: h j u l
Fifth set: d w e n
Sixth set: k q v x y z
This letter order, along with many other options and the teaching process is explained in great detail on one of my favorite blogs, Living Montessori Now. When introducing each set of sandpaper letters (that I made myself), I do the following:
1. I sit beside Reed, usually on the ground, with the new letters at my side.
2. I place one of the new letters in front of us. I slowly trace the letter with my finger (just as I would write it) and say the letter sound (for example, "a" as in "apple" or "b" as in "ball"). I try to make the letter sound as clear and natural as possible, no silly exaggerations or games. To review, if I was teaching the letter "s", I would : show the letter, trace the letter, make the letter sound (sssss).
3. Next, I have Reed stick out his pointer finger, and I hold his hand as I trace the letter with him, saying the letter sound clearly as we trace. I ask him to say the letter sound as well. I have also found that it works well if we talk about the shape of the letter. We talk through straight lines, curves, hooks, circles, and other shapes. He really likes doing this. Then, we are finished with that letter.