Start to think about how your potential customers might find you, don’t just target broad keywords like ‘cars’, consider local phrases such as ‘car dealers in Glasgow’ or longtail phrases such as ’used ford focus dealers in Glasgow’. Use the ‘Google Adwords Keyword Tool’.
Get active in the social sphere as soon as possible, use Twitter, Google+, Facebook, Pinterest, Youtube, etc. Social is now a major part of SEO and is a great way to connect with customers, you might also want to consider some social media management tools.
Start writing the copy for your site asap, the copy needs to be unique and user focused and a good length – 400 words+ is a good starting block for each page. When you write the pages don’t forget to write the META data as well.
A solid and internal link structure is a must, link certain keywords and phrases to other parts of your site that might be helpful to user. This will also tell the search engine what others pages on your site are about.