I don't change my set often at all. I had my Spongebob one for yeeeeaaaars. But, after like 4 years of not being around, I decided it was time for a change.
How I pick what the content is? It is a long and difficult decision. I think I told you that I wanted a new set about a month and a half before I actually decided what I wanted to change it to. It is usually some piece of media that I enjoy and also something that I feel would make an enjoyable-to-look-at image.