How to choose a monthly subscription novel

This probably seems like a stupid question but how do I find out about new graphic novels? Ive been reading novels for years but have always bought finished series, rather than monthly episodes.

Obviously I see the Batman, Superman, Marvel style comics in our local shop but where do I find out about the less popular ones.

I really love the horrible and funny style, particularly Garth Ennis (yes, I know) if anyone's has any recommendations 🙂