Search engine optimisation deals with several aspects of a site. The overall aim is to raise the profile of the site not just relating to search engine ranking but also to users. Just how much optimisation required will depend both on your overall objectives and how competitive your keyword or phrase is. You can achieve better ranking for your keywords but you need to ensure that your site will appeal to a visitor when they arrive. You would probably like them to want to come back too!
Content
Ensure that your site has text content. Your page content should contain your targeted keywords but make sure you keep in mind that it needs to be understood and interesting to your human visitors. Good content will eventually bring more relevant traffic as well as making it attractive for other sites to link to and so increase it's link popularity.
Structure
Your page should be 'spider friendly'. Make sure that there are no errors in your code, or broken links and that your navigation can indeed be navigated. Keep title & description tags relevant to your page and do not make them too lengthy. Remember it is these that probably make users want to enter into your site initially.
