When I first walked into my eldest child's preschool classroom, I was struck by how many labels and words I was surrounded by. Most objects in the room had a neatly printed label on them - window, chair, door, etc. The children in this classroom were exposed to words even when they were not sitting down with a book. There was a clipboard for them to "sign in" even though most of them did not even have the ability to print when they first started preschool.
From this experience, I realized that it is important to give children the opportunity to encounter letters and words on a regular basis. A laminated placemat with the alphabet on it, magnetic letters to play with at the refrigerator (or on a cookie sheet), alphabet theme puzzles, etc. All of these activities will help to strengthen letter recognition. Singing the alphabet song while playing adds to the fun.