Put the following in your .vimrc file and you are set:

au BufNewFile,BufRead *.yaml,*.yml set et ts=2 sw=2

When you will be editing YAML files, you’ll automatically have the following behaviour:

• et – expand tabs – puts spaces whenever you use tabs
• ts=2 – tab stop – 2 spaces per tab
• sw=2 – shift width – 2 spaces to move with < and > commands