Hi, from my personal experience! I can tell you that I get my medals for various contributions!
You usually have to do a whole lot before they give you a medal! Your chances of getting a medal sooner would be easier if you visit your favorite clubs practically on a daily basis and comment images,rate images,vote on picks,answer questions,upload images, etc.! You don't have to upload images to get your medal I have known some people to get the medals by simply commenting,rating and picking!
For me to get my medal it took a month of going to the club/spot everyday and participating in it almost everyday!
I hope this helps! I hope I get my medal here sometime soon lol! I have so much that I am a fan of so it will take some time to get many medals!
fanpop keeps the exact formula for how it calculates a dedicated fan secret, but just general participating and posting good content that fans give high ratings to seems to do it.