Besides visitors that are using a desktop PC, your website is likely to be accessed via laptops, tablets and mobile devices. Search engine optimization (SEO) for those devices should be a consideration in your strategy.
The first step to mobile SEO is to create separate keywords for your mobile website. You can use tools such as Google Adwords Keywords Tool to refine your keywords.
While you are thinking about using a separate section of your site for mobile users, consider using a subdirectory rather than a subdomain. The value of inbound links to the mobile site is doubled if it lives in a subdirectory, as it counts for SEO for both the main site and the mobile site. If you use a subdomain, it only counts for that subdomain, and not the main site.
If you aren’t already using one, create a mobile sitemap. Whether you are using a subdomain or a subdirectory for your mobile site, a sitemap specifically for your mobile area should be created.