Role of returning customers vs first time buyers is significant in e-commerce. In comparison to first time buyers they spend much more money (or time) on online shop or service. However returning customers usually are interested in some different aspects of your service or products than first time visitors. Using Google analytics it is possible to see what are URLs of landing pages for the two groups of customers. And usually the landing pages are different. It means, that onsite SEO techniques should differentiate between the categories of customers.
The onsite SEO techniques depend strongly on market/product/service, however general acceptance of this simple fact, that there are two groups of visitors, and that they have different needs is first step to increase conversion rate and improve general performance of web service. Generally, it is a good idea to find some techniques – such as improving user experience by optimized navigation – to change first time visitor to returning visitor.