Divya Kumar wrote one of the most insulting posts I have read in a long time, called, "How to... Be a pop-culture junkie."
I would like to suggest how the article should have gone.
Don't just watch, read, or listen to your favorite works. Immerse yourself into the mythos of the setting and the characters. Pay attention to the threads of plot, and join in the throngs of other fans who are trying to figure out where the story should and ought to go. Analyze the stories for deeper meaning as share your theories with others.
Stop just watching, reading, or listening to your favorite works, start participating in them. Look for vids, filk, fan fiction, and fanfilms, then take some time and make your own. Start or join a roleplaying group, and roll the dice. Find a convention near you, and go.
Every fandom has its own culture, and you need to learn the ins and outs before you can truly become a part of it. Many fandoms associate themselves with charaties, and certain kinds of special events. Read up and figure out how deep you want to go. Some fandoms are deeper than others, and their depth often ebs and flows, so figure out what kind of a commitment you want to make before you get swept off your feet.
Don't settle for the characters and stories you have become accustom too. Some of the best fan works have involved original characters and fresh new storylines. If you feel the urge, make some. If not, look for some others have created.
Watch what you are doing. It is easy to get carried away and spend more time and money on fandom than you intended. Set up a budget, and keep to it. Involve your friends and family. Friends you filk together, stay together. It is a great way to build strong bonds between your friends and family. Don't force it on others, but don't forget to give them a reason to participate.
That's how to be a fan
Did I miss anything? I've often thought about making a new fan primer. They used to have them, but the practice went away. Maybe it is time to bring it back.