Reading any book

Reading any book--whether you loved it or hated it or just didn't care--helps improve your writing. You learn what works for you, what worked for them, what worked in the past and what's likely to work in the future. You learn about yourself and your prejudices as a writer. You learn about what type of writing stimulates you and what leaves you cold. Anything, from the longest epic to the tiniest, most amateur blog entry, can have that sort of impact on you. If you know how to look at it, that is.