Just because a child can say or sing the letters of the alphabet does not mean he or she is ready to identify each letter individually all at once. Start small when you teach phonics, choosing one letter at a time as your focus. Pick a letter and write it down in several places around the room. Display pictures of words that begin with that letter, too; for instance, when studying the letter B, display photos of bananas and baseballs. Sing songs that have B words in them and practice saying the sound that B makes as you look at a picture of the letter B.
When children learn about rhymes, they practice identifying specific sounds and matching those sounds with other sounds that are alike. Let preschoolers practice rhyming when you read nursery rhymes together. Sing silly songs together and practice saying a word and then asking the child to identify another word that rhymes with the one you have said. To simplify this activity for a younger preschooler, give the child three choices of words and ask him or her to pick the choice that rhymes.
Children learn in a variety of ways. Enhance children's learning by teaching one particular skill several times and in different ways each time. Let children draw a picture of something that starts with a letter, then sing a song containing words that use that letter. Then ask them to point to that letter in the alphabet on the wall and later have them play a game where they go around the room pointing to things that start with that letter. Finish out the week by making a snack that starts with that letter or resembles something that starts with that letter. Engage children's senses as they learn and they will be more likely to remember the lessons you have taught. Phonics doesn't have to be about reading and writing only; there are many other ways to teach about letters and sounds.