I've actually been doing some writing, OMG. (Co-writing an original fic with a friend. It is writing, and it's been way too long since I last did any of that.)

I include OCs in longer fics, and I find I like to tell a known story from a different perspective, which is very often that of an OC or a minor character. I think a lot of it depends on what the story is - sometimes I want to explore a facet of a known canon character and sometimes I want to show how a canon event appeared to others involved in it. Those fics do tend to be the longer ones, though.