Well, for myself, I do like to experiment. I have yet to create a character similar to another to such a point that they are nearly identical, mainly because I cheat a little....I tend to bend but not break a rule most authors set for themselves, that "editted self" or "self insert" rule.
I don't create self inserts, but instead, I take "packets" from myself in order to create OC's.
All of my OC's have something in common with me, it might be an event in their past, or a certain quirk in their personality. I do this as a way of grounding them. I can relate to them easier and put myself in their shoes more effectively that way, I can think like them, so I tend to make characters that end up being more on the low powered side, but whose personality are more like a real person's.
(Of course, I don't leave my OC's powerless...)
I also borrow a lot from the literal hundreds of fantasy books I've read. I have a very wide knowledge of different types of magic and creatures, so I put that to use when creating OC's to make something unique.
As for OC's I get rid of quickly, those I tend not to elaborate on. Makes um easier to get rid of after all. Those that I do expand on though...they end up going out in a more violent/elaborate way than I originally planned.