Most books for beginning readers have words with the most common sounds of letters.
The short vowel sounds are the most common and are in words that are easy to read. These words follow the CVC rule and the VC rule.
The hard sounds of the letters c and g are what I teach first, like in cat and goat. (not circle and gem)
Here's a free Nonsense Word Test I created to check if a beginning reader can blend the most common letter sounds and read nonsense words. (You can make two copies of this test and circle the letters missed on your copy while a child reads.)
If a reader doesn't know letter sounds,
letters will not be helpful for reading!
Take some time to play with and teach letter sounds and get some good books to practice reading.
I really like K5 Learning. There are some great early reading tutorials presented in a variety of ways.