Have a complete set of alphabet blocks. No matter what language you are teaching, make sure you have a complete set. They can be easily misplaced--especially by young children--so it is important to have a bag or box where they are stored between play times.
Encourage play with the blocks. Remember that play is a child's work. The reason alphabet blocks work as a learning tool is that they are fun and educational at the same time. Allow your child to stack the blocks, make patterns or just practice holding them. During this play time, point out the letters or words on the block by saying things like, "Oh, you have the A block and I have the B block. Can you find the C block?" This encourages them to recognize the letters and be able to pick them out.
Put the blocks in alphabetical order. Make a tower or a long train with the blocks in order from A to Z. Don't do this yourself, but help your child to do it. At first you might only get through the first few letters. That is OK. Each time you play, try to add a few more blocks until your child can help you put the entire alphabet in order.
Make words with the blocks. This is not necessarily to teach reading, but to show that letters can come in different patterns. That way, your child will be able to pick out letters even if they are out of alphabetical order.
Use sounds. If your blocks have pictures or colors on them, point these out to your child. Say things like, "This block has a mouse on it, and mouse starts with mmmm, the letter M!" Practice these phonics with your child by having them tell you what sounds a letter makes, not just the name of a letter. Some letters make more than one sound, and you can talk about that, too.
Let your child direct the play. After you have completed your "lesson" let your child teach you or have free play with the blocks. Often, they will repeat some of the things you said or did, and this repetition will help cement the new concepts in their brain.