If a child is attending kindergarten, the teacher has probably assessed his or her reading level and has the child reading books that are appropriate for that level. Ask the teacher what the reading level is. Books are clearly labeled with the reading levels, so you can purchase ones to read together at home. Some teachers recommend that books for home be one or two levels easier than the ones at school.
If the child is at the very beginning stages of reading, and knows letters and most of the sounds but can't always sound out the words, choose books with pictures that clearly illustrate what is happening in the text. When children first start reading, they can use the illustrations as clues to help them figure out what the words are. As they learn more words, choose books that have appealing illustrations that don't necessarily give clues as to what the words are.
Choose books with repetitive text, perhaps repeating a few of the same words on every page. This way, once children figure out the first page, they'll be able to read most of the other pages in the book as well. The repetition helps children remember words, and reading a whole book will increase confidence in reading ability. Some books also replace a couple of words with pictures, and have the words written underneath.
Let children hold the books and turn the pages. This provides a sense of control of the book and reading. Have them put a finger underneath each word as they read to help teach that reading goes from left to right, that each group of letters makes a word and that each group of words makes a sentence. Don't offer words too quickly if a child struggles. Ask him or her to look at the first letter of the word, sound it out and look at the picture for clues. If kids still can't figure it out, then supply the word.