.gitignore file setup for Acquia Cloud
Acquia Cloud provides you with a default .gitignore in your repository (as described here):

docroot/files
docroot/sites/*/files
docroot/sites/*/private
acquia-files


It usually is enough for the vast majority. You're however free to add anything you don't wish to keep under version control. There's no perfect setup and it really depends on what you'd like to achieve. I strongly suggest keeping settings.php under version control because it holds critical configuration for your site.