Proofread a short comic story

I have a short comic that I have written as a promotional piece for a game I am developing. It is currently approx. 2500 words long but the bit that I really need to get right is the dialogue. I have an artist waiting to draw this up but I want to ensure there are no spelling mistakes and that grammar usage is correct? Also it make sense needs to.

Preferably like someone with a bit of experience with comics/graphic novels as I have none :)