Ah... I don't exactly have a strategy. I've licensed art (and writing) under CC0, CC-BY and CC-BY-SA alike, based on a rough feeling of how much effort went into it and how much potential for reuse it seems to have. Many people are happy to provide attribution if they can, even if it's not required. And releasing lots and lots of stuff under a very liberal license can make one very popular if word gets around. ;)