Each month we do a monthly competition for the best articles (as voted by the community) in six categories: C#, C++, Web Development, Database, Mobile, and Everything Else. The voting is visible on the home page for two weeks. We start the voting for a particular month's set of articles the following month. For example, we would run October's competition in November. We try to start the voting approximately one week after a new month begins to allow articles that were posted later in the previous month a chance to get some votes.
Articles for the monthly competition are chosen primarily by article rating, article popularity, tags, and how appropriate the article is for the category. In some cases, for example, you may see an article that simply used a lot of C# code in the C# category, but ideally each article is focused as specifically as possible on its category. You can see how article rating is calculated here. Aricle popularity is calculated by:
$Article Rating \times \left ( \log_{10}NumberOfVotes \right )$
Tags are fairly self-explanatory. If you want to be considered for the C# category, you must have a C# related tag in your article. Other categories are a little more broad. For example, if you want to be considered for the Web Development cateogry, you must have at least one tag related to Web Development, like IIS, ASP.NET, Javascript, CSS, HTML, PHP, MVC, jQuery, HTML5, Knockout.js, AngularJS, etc.