Most importantly, the book was interesting. It doesn't have to be artistic. If your child is very curious, perhaps he likes to read encyclopedias. If the child has some passion, such as he loves planes, get him a book about airplanes. Be attentive to your child's interests, because you play an important role in discovering talents and abilities of your child.
The next step is to determine the difficulty of books to read. Ask to read your son or daughter the first two pages of the book aloud. Evaluate how slow the child is doing, how often read a word incorrectly, how often puts in words the emphasis on the wrong syllables you need. If in 30-50% of cases, the book is too difficult.
If no errors at all, it is too easy. You need to pick up a book that was not just interesting and informative, but could also improve reading skills.
Don't forget to ask the opinion of your child about the book. Ask whether she liked him, what new did he know? Ask them to retell the content. Try to look genuinely interested in the story. Your interest will help your child better remember the content of the book, and also to feel more intelligent and confident, but these feelings are the best motivation for reading new books.