I haven't really played around with this concept a whole lot, but I found that using astrology to help define a character can be very helpful. What I would do was decide which astrological sign I felt my character could identify with the most by searching up all of the signs on Wikipedia and studying the traits associated with them. I probably wouldn't use every trait, but I'd definitely draw inspiration from most of them. For example, if I chose my character to be a Gemini some of the associated traits include: charming, intellectual, over-talkative, and ego-oriented. What is also cool about Wikipedia is that it shows you the positive traits and the negative traits the sign has, physical traits, ideal careers, likes and dislikes, and which signs you are and are not compatible with. This idea was super helpful for me and I thought I'd share it with anyone who may be struggling with new characters.