Aim to have your child read for (at least) fifteen minutes every night before bed. Don’t forget reading during the daytime, e.g. at weekends rather than watching television. You don’t want your child to think they are only ‘allowed’ to read when they’re in bed! Also make sure they have a bookmark; they won’t be able to read the whole book in one go, and you may find they don’t want to stop.
Start them on a book which you think may be too easy. It is better for your child to have the warm glow of success than the horror of being over-faced. Books are rated roughly by age: 5+, 7+, 9+ etc, but this can be deceptive. Publishers seem to think children are reading fluently the minute they turn 5, which most aren’t. Go to the Reading List.