Reading other people's writing is so important to the writing process. It's one of the first tips I'd give a writer starting out. It really is the best way of picking up tips.
For a start you'll learn new vocabulary, new phrases that'll better populate your works. The choice of words is so important to make your story flow and not be a repetitive process. You'll discover different ways to write. Dan Brown and Charles Dickens are both authors who wrote for the mass market, yet their style is so different. Dickens wrote his stories as instalments, therefore there were lots of hooks to keep the reader buying the next magazine. Brown uses suspense to keep the story rolling.
Reading also opens new worlds up for you. Narnia, Middle Earth and Earthsea are all different. Beautifully crafted worlds that are inhabited by believable characters. Reading allows you to see how to construct your own world.
So a writer must read and read as widely as possible.