Drupal out of the box has good SEO features that makes it Search Engine Friendly (SEF) instantly, just converting a website to Drupal has positive effects on the SEO side. With good themes that have SEF markups and things like javascript (JS) and CSS aggregation in Drupal core it helps to speed up a website and attract search engine bots. Core modules like path helps to define SEF URL for the content of your website with clean URL without the ?q=. If you have path on, I guess the obvious next step is to get pathauto, so I will not include pathauto in my list below.