There's an interesting post over at Fangs, Fur & Fey asking what people read while they write. Some of the respondents have said that they have to read outside their own genres while they writer, and some of them have said that they don't read any fiction at all while they write, which, wow.
I personally am a constant reader. There's no way I could stop reading while I wrote or I would either (a) never read again or (b) never write again. Even when I was in law school, I read all the time.*
But I do have to be careful about what I read when I write, because I am a person who picks up style very easily, and if I read something too distinctive, then it can end up influencing what I'm writing whether I want it to or not. So, for example, I can read anything by Stephen King. Fiction, non-fiction,** he is style neutral for me, I think because his own style is so natural. He has his tricks and tropes as we all do, but it feels natural to him, and so it feels natural to me. I prefer earlier Stephen King, up through and including It and The Dark Tower.
Actually, now that I think about it, I can read anything that is non-fiction. For some reason, even if it's very stylistically unique, like David Foster Wallace, my brain thinks "oh, it's non-fiction. It doesn't apply to you," and I can read away. I cannot, however, read DFW's fiction while I write, because it will infiltrate my brain and everything will come out overly wordy and feel like it needs twelve footnotes to explain it.***
I can read some writers who are better than me. Jane Austen. Anne Tyler. Tana French. Most YA writers. Many others. I don't have any of that Harold Bloom anxiety of influence stuff going on. Reading a good writer can actually help me elevate my game, but it really depends on the writer. Some, like DFW, are no gos, not because they awe me with their skills, but because they overwhelm me with their styles.
I cannot read books that suck. Obvs, I'm not going to name names here, but there are certain books, and certain writers for whom I have to have at least a four hour cushion between me reading their stuff and me trying to write anything creative. For some reason, bad writing sticks in the style center of my brain a lot longer than good writing.
For that same reason, I often don't try new books or new authors if I plan on writing in the next couple of hours. It's just too risky. A book that is too stylistically unique (or too bad) is just going to gunk up the works, so I'll read The New Yorker or something familiar instead and save the new books for after I write.
* True story: while I was in law school we could take up to 9 credit hours in other departments and have them count for credit. Several people took dance or some other form of physical activity. A couple of people took foreign languages. I took 18th Century Novel. Yeah, that's right. The first book in the class? Clarissa. The longest novel in the English language. I say this not to remind you that I Love Long Books, but to demonstrate that reading is like breathing for me. I do it all the time and it never seems like work...unless I'm swimming.
**I really like his book On Writing. It's not ground breaking, it's just the story about how he did it. I find it encouraging.
***I do not think that DFW is overly wordy, just that when I do him, it is. That's the difference between his style--which seems natural to him--and my poor imitation of his style.