Directory submission Article submission Blog creation Blog promotion Rss feed book marking social media optimization forums posting ofcourse all of them!! One more activity u can try that is "Exchange Links"
Blog commenting, link exchange, profile creation. Those are also some ways where you can get backlinks.
they all are good activity for seo if u want to get more back link you do link building with good pr websites. and do high pr directory and after that u can get back link...........