I had mentioned before that when I am teaching sign language with phonics I do it in conjunction with the Houghton Mifflin Sound Spelling Cards. Here is a link to see what the cards look like. You will notice that this is a pdf file that was created by another school district which shows recreated Sound Spelling Cards. That is because you are not able to reproduce the actual materials from Houghton Mifflin (HM). You can buy them for $139 if you like!
When you look at the cards you will see that there is a picture for each card, and the various spellings for each sound. I like that these cards show you ALL the variations for how the sound can be spelled, unlike other letter cards that just show a picture and the letter. This is another reason why when I teach the sign for each card I use the picture, not the letter handsign.
For example, look at the letter C card. It is a picture of a cat. I would have the card hanging on the wall and say "C as in cat says /c/, /c/" and sign the word cat as I am saying this. Then, I would stop and explain that C can say /c/ on its own, or the best friends CK can also say /c/, but only at the end or middle of a word.
I would usually teach about one sound/spelling card every 3 days or so until it was mastered. Then as I add in new ones to teach, I always end the lesson with a review of all the cards I have done. I would suggest that you align your lessons with the language arts adoption that your child will be using in his elementary school. If you are not sure which program they use, just call the school and ask. You can always create your own too, but why not give them a head start!