When I first started using Vim as my full time editor, one thing that tripped me up was copying and pasting to and from Vim where I run it in the terminal. Line numbers wanted to come with my copys, and indentation on code went wacky with my pastes into Vim. A couple quick, temporary settings changes, though, and Vim handles everything just fine.
When pasting to Vim in the terminal, if line indentation gets out of hand, progressively indenting each line. Fix it by turning paste on: