Once your child has learned to recognize all the letters of the alphabet, you can start working on letter sounds. My two children have very individual learning styles so I have used different techniques and resources to help teach them their letter sounds. My son Jacob is a kinesthetic learner which means he learns best through hands on activities. Rosa, on the other hand, is an auditory learner. She learns best through activities that involve listening, especially musical activities.
Rosa recently finished learning all her letters, so I was on the look out for some auditory learning resources to help teach her letter sounds. I came across a wonderful video from Leap Frog called The Letter Factory. This video has become a favorite of Rosa's and after watching it four or five times she knows almost half her letter sounds. I would not usually recommend a video and I want to add that we have an hour a day limit on videos and computer games in our house. This video is a cut above most of the videos that are advertised as being educational. It teaches the letter sounds through cute story lines and songs for each letter. It is the songs that seem to really stick in the kid's heads.
Back when Jacob was learning his letter sounds, I found a book called Games for Reading by Peggy Kaye. This book is a wonderful resource of fun activities to help teach pre-reading and reading skills. We used two games in the book to teach Jacob his letters and his letter sounds. One was an egg carton toss game and the other was a game called "hop on it". This was a game we played outside on our paved driveway. I wrote different letters all over our driveway using sidewalk chalk. I would then call out a letter sound and Jacob would have to go jump on the letter that made that sound. Often I would pretend to race him to the correct letter or try to hold him back so I could win the round. He thought that was hilarious and he wanted to play "hop on it" over and over. This game can also be used to learn the names of letters as well.
There are many ways to teach concepts to a child and what works for one child will not necessarily work well for another. A teacher in public school does not have time to teach each lesson using all the learning styles (visual, auditory, and kinesthetic). If you see your child falling behind in school, it would be a good idea to supplement his learning with fun activities at home that are geared to his or her learning style.
I should also add that I tried playing "hop on it" with Rosa to help her learn the letters and she wasn't into it. It just wasn't her learning style!