Search Engine Optimsation is the process of improving your ranking in search engines. There are all kinds of small things you can do in your HTML to improve your chances of getting a higher ranking, like: specifying meta tags for keywords & description, always specifying meaningfull titles. For more information see Google's Search Engine Optimization Starter Guide and webmaster guidelines.
Below are a few easy steps you can do to optimize your site without much effort. First of all Microsoft has a toolkit (currently in beta 2) called the Search Engine Optimization Toolkit. You will need IIS 7.0 or higher for this to work (Vista, 2008 or higher). Beats me why you need IIS 7 because you can use it on any site, not only the ones hosted on your IIS.
Anyway it will integrate into your IIS management console and it will give you the ability to analyse your sites for SEO. After it finishes it will give you a very detailed report of errors and violations.
If SEO is important for your site I would recommend to regularly run this tool during development and production and fix as much violations and errors as possible.
Furhtermore you might improve your results in Google by submitting a sitemap.xml which can be easily generated online and creating a robots.txt which can be created in Google Webmaster tools using Crawler Access.