There is a correlation between Alexa Rank and sites who appear in search results often. Alexa measures and monitors a site’s popularity based on traffic. If you are in the top 100,000 sites, you are considered to be a popular, trusted site with a diverse amount of traffic.
Generally speaking, if you are a top rated site with Alexa, you should be doing well with your SEO efforts. Your site is probably ranking well for competitive terms, you have a steady stream of fresh content, as well as a diverse amount of visitors from all over the world.
There isn’t much you can do to affect your Alexa ranking, except continue to build good content and valuable links. If you do something very viral, Alexa will show the results pretty quickly, as their rankings change daily. This means on one viral video posted on your website, you could go from greater than 1 million rank, to within the top 100,000 in one day.