For a successful site the following things are considered imoportant from SEO point of view.
I am laying down some of those important ones for your referral.

Suitable Meta Tags for the pages related to the keywords.
Placing Keywords Tags for the pages related to the keywords.
Images of car models with non-descriptive Alt Tags.
HTML and CSS Validation.
Content Optimization.
Web Site Internal Link Analysis.
Limiting the size of the pages especially the home page.
Directory Submission of this site to 200 web directory.
Decreasing of the load time of the page.
Maximizing the CSS to decrease the page size and make it search engine robot friendly.
Blogs related to the products or services offered by the site. This helps bringing qualified traffic to the site.

These are some of the SEO checklists that must always be kept in mind before starting off any SEO based project.