A lot of Vampires are placed in Victorian clothing in certain stories.
I think this kind of dress could work.
Or something similar to this.
Or that maybe.
These are nice looks, and I think they could easily translate to vampire. I think a good idea is to stay away from cliche "black and red" color scheme. It's very common in Halloween costumes. Maybe even stay away from black entirely and go for a different color scheme?
I'm just shooting in the dark... it's hard to guess what you might want for your style so I'm just throwing out ideas.