As some of you know, I spend more time developing than actually writing and in some cases it's in excess, but in some cases it's for legitimate reasons. Most of us have probably heard about personality types - I remember a very popular quiz
(12+) that told you which Harry Potter character you were based on your type! (this is a very simplified quiz, not meant to be completely accurate) - but they're really a lot more in depth than labeling people as "smart" or a "people-person." Anyway, they're all four-letter combinations that allow for 16 distinctive personalities. Once you find yours I think it's pretty clear that it's a good fit; mine was me to a T. :)
So, what does this have to do with OCs? Sometimes it's hard for me to come up with characters without basing them off of people I know, so this is another good resource aside from real life that I find really interesting. It can help if you have some characteristics in mind and want to expand but don't know where the depth is going - for example, my type, INTJ, is on the surface a person interested in ideas, academics, making things better, etc. But we tend to stay up late thinking about things rather than sleeping, don't like to be leaders except when the current administration isn't effective, don't get into serious relationships until later in life, aren't impressed by catchphrases, etc. Once you find the right type for your character it's easy to find plenty of analysis online.Here
(12+) is a good starting place. Let me know if this is at all helpful - it certainly inspired me to go analyzing each of my mine characters!
And of course, remember that quirks belong to your character and no one fits a type exactly, or else the world would be really boring. ;)