When a child is learning the alphabet, it is not enough to merely show them the alphabet and expect them to learn it. A child has to be shown something in several different contexts in order to retain it. Before you can even teach them the alphabet, you should teach them the sounds of lettes. This lets the child understand that letters make sounds, sounds make words, words make sentences and sentences make stories. It is a natural transition. When you move onto naming letters, be sure to restate the sound each letter makes.
They need to see it, feel it, taste it, explore it. That can be intimidating for parents but there is no reason to worry. Just be sure to teach your child in a variety of ways. Don't panic, there are several ways to teach letters that are inexpensive and not overly time consuming.
First, you can show them a printed letter. Do not just show a flashcard, show them the printed letter in a variety of ways. Some examples, the aforementioned flashcard, a magazine, a street sign, etc.
Next, let them write the letter using hand over hand. If you have an easel, this is a great way to work on the letter. Put the chalk into your child's hand and then put your hand over their hand, now write your letter. If you have the easel chalkboard, this is great to work on wrist strength and an important skill for your child. After writing on the easel, you can also practice writing on a pad of paper on a table. This works the child's muscles differently and is also important to their development.
Now, pull out the play dough. Teach him how to roll out a "snake" and then work on forming the letter with your play dough snake. At my house, we have the "Roll-A-Dough Letters" from Handwriting Without Tears. This is a great product and we love it, but it is not necessary. This can easily be done at home. Our kit involves a tray, letter cards and dough. My favorite thing about the kit is that it shows you with an arrow, where to start making your letter. My least favorite thing about the kit is that the dough crumbles when you try to make it into a snake. We usually just use regular play dough.
Another tool that we use frequently is our Sandpaper Letters. You can purchase these online for around $30-$40 or you can check out Momtessori for directions on making your own sandpaper letters. She uses foam board for her background and then uses a die cut machine to cut the letters out of sandpaper. I have also seen them made with sand sprinkled over glue and with glitter glue or puffy paint. The thing I love about our Sandpaper letters is that there is a hole punched in the sandpaper to show you where to start tracing your letter. This can be done when you make them at home, or you could draw arrows with numbers, showing the direction to trace/write.
We also use our alphabet cookie cutters a lot. I do not bake a lot of cookies, but I use the cutters for anything. If my son wants cheese and sandwich meat (think homemade Lunchables), then I use cookie cutters to cut out the food. I also use them for cutting fruit or anything else. Cookies cutters are not just for cookies!
Another fun thing that we did is go around the house and take pictures of people and/or toys for each letter of the alphabet. I then assembled the pictures in an album and put the first letter of each word in the sleeve with each picture. This helps with the phonological awareness, as he already knows how to pronounce all of the items that I have taken pictures of.