Both On-Page and Off-Page SEO are important in SEO
On-Page SEO techniques:
keyword research and analysis
content writing
use of meta tags, alt tag, h1 tag, title tag in HTML codes
submission of sitemap.xml and robots.txt
submission of website/webpage to Google Webmaster tool for indexing
internal linking etc
Off-Page SEO techniques includes linkbuilding in:
Directories submission
Article submission
Press release submission
PDF sharing
Blogging
Forum etc