Part of eliminating the comic book-ie feel of the villian would be to not make a stupid villain like Billy Zane in Titanic that is just annoying and bad all the way thru which would make the audience wonder what ANYONE would see in that guy.
To make a life-like villain you have to create a character who isn't all bad all the time. He has to be a controversial figure. One of the best movie villains I've ever seen is probably Robert DeNiro in Godfather Part II. He should be a person that you can see why people would be drawn to him, or Forrest Whitaker in the Last King of Scotland... Controversial realistic villains are the only ones that would make sense in the real world. Otherwise, if they were Loki all day, they would have no allies at all. "Oh I want to bring darkness and destruction....." and then what? "hmmm I don't know... " that is kid stuff.