There's a lot of good advice in this thread already!
I will second the idea of, having a strong pitch, and paying your artist. Having a contract will help too, of course.
I think it's also important that you work hard on certain aspects so your artist doesn't have to: that is, interacting with readers, making advertisements, trying to get reviews, running the social media, etc etc. Art takes a HUGE amount of time, way more than writing does (I say this as someone who does both) so make sure it feels like you're a partner in this and that it's worth while to work on your story in particular-- especially if you can't pay your artist at industry standard.
Good luck!