Although we take it seriously, there's no secret sauce here. We pick pens/projects/posts/collections as they come in, based on what's looking good that day. Sometimes we'll go with a theme (like on international panda day - thanks Marie!) like so:

We have a few trusted non-employees who have picking capabilities turned on. Picks are added to a queue and are rolled out every 20 minutes. I can be bribed to pick you pen with thai food gift certificates.