Here are some great tips from Scholastic for encouraging your reluctant reader. It's important to take the pressure off a child who struggles with reading, or doesn't read for pleasure.
I'd also add, try audiobooks! Sometimes a child misses out on a great book or series friends are reading. I've seen students check out Harry Potter, a book they'd really struggle reading, just to carry it around so they looked cool. There are lots of great audiobooks out for all ages, so help your child browse for what he or she finds interesting.