Hello Friend, first you should select keywords and than after do onpage in perfect way and then you can do off page by article submission in top article directories and directory submission, forums posting , social book marking, blog commenting etc.
To start Seo for zero rank site we must judgment what types of on page required of that site then generate back links for that site as much as possible.Back links is the major factor.
For the site ensure on-page SEO: Whereby the keyword is in the title, description, and meta keywords, as well as naturally in the content, and for off-page SEO ensure the backlinks you are getting be it from article directories and others have your anchor link (your keywords you are trying to match when you did on-page SEO)