Stolen from this site. Definitely worth a full read.

<C-d> and <C-t> indent back and forward in insert mode

The normal mode equivalent is >> and <<

I typically use == for auto indentation but this comes in handy when you want to be explicit or there isn't any autoindentation

Using the detectindent plugin, indentation is automatically detect indent based on what is already in the file (expandtab, shiftwidth, tabstop settings)

:autocmd BufReadPost * :DetectIndent