Everyone has heard “write what you know.” How people define “know” is, of course, variable, but it is fair enough advice on the face of it – if you don’t know about sub-hunting in WWII, don’t write fiction about sub-hunting in WWII because it’s going to come off as inauthentic. That’s not to say you had to hunt subs in WWII or that you need to be the leading expert in that field, just that you need to have knowledge of the subject to make the fiction convincing and authentic.
I would suggest we also add “write what you read.” This is part of “write what you know.” If you don’t read hardboiled detective fiction, don’t try to write it. If you don’t read sword & sorcery fantasy, don’t try to write it.
Every genre has its tropes as well as its clichés, and without reading them, you probably won’t know which is which. You also won’t know what has been done in the genre, and what has been done to death. You may believe you have a fresh take on the genre, but without reading widely in it, you honestly don’t know. You are making choices based on assumptions, and we all know how well that usually turns out.
Some writers don’t want to read in a genre as it will taint what they consider their fresh perspective. If so, than it behooves that writer to look at scholarly works on the genre or otherwise learn about the genre if they refuse to read it. Still, if one’s voice is so distinct, should one fear reading in the genre? Relying on retrospectives or inventories of works in a genre is kind of like taking a Ph. D. in Korean History and refusing to learn Korean – you are relying on interpretations and translations rather than primary sources.
I think the only way you can write fiction that can impact on a genre in a positive way is by knowing that genre. This does not mean you must adapt to it, it just means you have surveyed the beach in which you are going to swim so if you appear without your bathing suit it is because it is actually accepted in that area rather than because you assumed it would be.