What are best practices for Drupal 7 my.conf settings?
You need to profile this yourself, every server is different - there's not really any such thing as 'best practice' here; get mysqltuner up and running, and follow the recommendations. 

Don't try to think of it in terms of Drupal, rather in terms of any web application which needs optimising. If you get too hung up on the 'Drupal' aspect you'll end up looking in the wrong places to optimise