Search preschool websites for activity pages focusing on letters of the alphabet. Print out a letter each week. Help your child color the letter however he'd like and hang it in his room.
Pick a letter each day and serve snacks that begin with that letter. For "A" day, set out apples, avocados and artichokes. Reinforce the lesson by asking your child to locate the letter of the day among the alphabet magnets on the refrigerator.
Go on a letter adventure. Take a nature walk and point items that start with the letter you choose. For instance, choose the letter "T" and find a tree, a trail and a truck.
Read alphabet books together. Books help children learn to recognize letters, and hearing you read words helps them learn the sounds of the letters.