Try reading a book together, with you reading the first chapter or first few pages to draw him into the story.
Model for your son the process you go through when you read. Comment on twists and turns in the plot or how you get information about the characters in the story from things they say and do, or things others say about them.
Try play-reading together, with each of you assuming different roles. Curriculum Associates (1-800-225-0248) is a good place to look for plays. Have a look at the Reader's Theatre series, for example.
Ask your school librarian for suggestions for books that your son might enjoy. Many boys, for example, really love books by Jon Scieszka. Check out his website for suggestions.
Many school districts or libraries hold contests during the summer months where kids are rewarded for reading books of their choice. Check with your son's teacher to see what's going on in your school.