I prefer using the vim-trailing-whitespace plugin and fixing it manually: https://github.com/bronson/vim-trailing-whitespace

Or you can use my competing plugin: https://github.com/bitc/vim-bad-whitespace

which has some advantages (described in the README)

One advantage taken from the readme:

  This plugin is better than using the builtin vim 'list' command because it
  doesn't show an annoying highlight while you are typing in insert mode at the
  end of a line.

Or, if you prefer a more manual approach (ie. my fellow paranoid developers) simply use `list` and `listchars`:

    set list
    set listchars=trail:•

In other people's code, use `set nolist` to prevent hyperventilation.

In general, explore `help list`.