How do you automatically remove the preview window after autocompletion in Vim?

Put the following in your vimrc:

" If you prefer the Omni-Completion tip window to close when a selection is
" made, these lines close it on movement in insert mode or when leaving
" insert mode
autocmd CursorMovedI * if pumvisible() == 0|pclose|endif
autocmd InsertLeave * if pumvisible() == 0|pclose|endif