Please note that Google's search results pages typically offer both paid advertising services and free organic search results. Listing in the organic search results is free, and using Google’s advertising services will not improve your ranking in these results. Free resources such as Webmaster Tools, the Official Webmaster Central Blog, and forums can provide you with a lot of information on how to optimize your website for organic search. Much of this information, along with details about paid search options, can be found in the Google Webmaster Central.
Before starting to look into SEO, it might be helpful to learn some basics and understand how search engines work. It is recommended to start with the following:
Google Webmaster Guidelines
Google 101: How Google crawls, indexes, and serves the web.
If you're considering hiring an SEO, it's best to start early. The ideal time to hire is when you're planning to redesign your site or launch a new one. This way, you and your SEO expert can ensure that the entire design of the site is optimized for search engine functionality. However, a good SEO professional can also help you improve your existing site.