There are endless ways to practice letter/sound recognition. Here are two of my favorite ABC preschool activities:
ABC Scavenger Hunt -Have preschoolers search for items that begin with the letter you are working on. List or display in a prominent area.
Alphabet Soup - Decorate a paper bag with an ABC theme to use during circle time. As you work on a certain letter, place items that begin with that letter in the bag. Have preschoolers close their eyes, reach in the bag and guess what they have grabbed based on how it feels and the letter it starts with. Once they are comfortable with the letter you can increase the difficulty by placing some objects that do not start with the correct letter and have them tell you whether the item belongs in the bag or not.
As you are learning about letters and making an ABC book, don't forget about the great alphabet books already out there.
Aardvarks, Disembark! by Ann Jonas, Eating the Alphabet by Lois Ehlert, and Pedro, His Perro and the Alphabet Sombrero by Lynn Reed are good books to start with.
You can also find how to make a preschool alphabet book, right here at Bright Hub!