First, allow me to point out that search engines don't rank websites. They rank web pages. So even on a microsite, each page ranks according to its own merits. Still, all the rules of SEO apply to 3-page websites as to 1-page sales letters and 10,000-page megasites. In essence, it doesn't matter how many pages your website has. It can earn good search rankings.
In some ways, it's more challenging for a microsite. You don't have any internal links. Well, you might have a few, but those few aren't really going to build you any link popularity. Of course, you won't have any search engine saturation either. But all you need is one good search ranking with a high volume of traffic.
Internal link structure aside, however, you can build a highly optimized web page and build links to it using a blog, articles, social media, and other traditional Internet marketing tactics. You do the same old things. You just might have to put a little more effort into them. Then again, while the challenges may be bigger for microsites in certain ways, in other ways the challenges are smaller. You have less to promote so you can spend more time doing the most important thing - driving traffic.
