One of the biggest mistakes a writer can make is not reading other authors' works. Reading is an education, we learn to spell and construct sentences from reading, we learn new words to add to our vocabulary and another way of speaking perhaps. It doesn't matter what you read, a picture book, a comic strip, a tabloid paper or literary works as long as you read something. People love to escape in fantasy, science fiction and romance and others prefer an autobiography or factual reading, it's all out there to be enjoyed.
For the writer, reading is essential to avoid becoming stale. But what of the writers' who say "I'm too busy writing to read!?" You have to study your craft, improve all the time, stay on trend if you write commercially and the best way to do all of these things is to read varied material.