Listening is Hard

I have watched some U.S. drama series*,like Friends and Vampire Dairies.These dramas are helpful for improving my English improving.But I feel find it very hard to listen clearly and understand the lines/dialogues. Maybe the lines are so/really local and very colloquial. Moreover (this is a bit too formal)/Besides/What's worse,/And some of the roles /actors speak quickly and casually---especially Damon in Vampire Dairies, I think. I like U.S./US/American drama/dramas/series and I will keep on watching the these series/dramas/them.

*Vampire Diaries is a drama series, but Friends is a sit-com.