Despite what many people think, SEO (search engine optimisation) cannot be something that is done once on your website and then left. SEO needs to be ongoing and with new updates being released by the search engines such as Google, your SEO may need to change or adapt to fit in with the latest algorithm.
When your site is first ready to go live, it is important to insure that all of the search engine optimisation has been completed to a high standard, such as Meta data, title tags, links and content etc. Over time you will probably add to and change your website and it is vital that you also update the on page SEO elements. Adding fresh content to your site is a big part of the ranking algorithm set by Google and these pages need to be relevant and unique in order to get ranked highly. Building up your pages and relevant content on your site will not only help you get ranked for more niche search terms but can help your overall positioning on the search engine results pages. Also being active on the social media sites and getting quality links back to your site is another way of pushing your site up to the top.