Effective off page methods:-
(1)Blog Commenting
(2)Forum Posting
(3)Article Submission
(4)Social Media Marketing
(5)Social Bookmarking
(6)Directory

SEO & SEM are for two different purposes. SEO is for getting higher rankings on search engine results while SEM is for targeting the traffic of the search engine viability.

In Short,
seo is free and long term process.
sem is paid and short term process.