Just because Twilight did it, doesn't mean you should. I have read excellent stories that are Vampire/Werewolf novels. However, those are really freaking hard to find. And trust me, it's NOT just the bloodsucker genre that tweaks my 'beard'.
I guess my point is, make your charecters shine. Make me love them or hate them, make me feel their emotions. Grasp me with the depth of your story, and don't try to mimic a popular success story.
Make it yourself.
I will admit I do have my own novel, Illumi, which IS a Werewolf and Vampire novel, but I am trying to incorperate unique situations within the story to make it... well, more unique.
I hope you all have a wonderful day, and if you're a fellow writer, I hope you take it into consideration what it is I have said.
And just one thing,