Off page SEO or search engine optimisation is doing things off site to improve your sites search engine rankings. The only thing you can do off site to incraese your rankings is build up more links. More links will generally lead to better Google PageRank and better search engine rankings.>
When you are trying to get more links you need to think about quality, not all links are created equal and links from low quality sites will have little or no impact on your rankings. The best types of links that you can get are from trusted sources such as universities, newspapers and even some of the top notch directories such as dmoz and Yahoo.