If that song the original post is to be about vampries and darkness make it less repetative and more bad ass. Do some more research on vampires and find some niche story about some vampire no one knows about yet and use that as the basis or something. Also think what the message or story of the song might be. ANd tell it through clever words worked out or just be blatant about it. Either way choose your words carefully.

Though I have found the more fun you have with writing the better the lyrics might very well be in the end. It's also good to write some stuff out then come back to it in a week then go over whether or not you like them anymore. Cause you might think hey that sounds bad ass now, and then you read it a week later and it sounds lame as hell.

Just been my experience with lyrics. Though there are plenty of funny death metal bands n such with hilarious lyrics muffled under bad ass music. Especially Emperor.