Hm. Tips, you say?
Well, I am usually startong character planning from their biography. The events from childhood can influence deeply, so if you want any fears or any kind of deviant behavior for your character, then it must take roots from their childhood.
Example: One of my characters snaps out in berserk mode if he feels any threat; he can't control it, even though he understands that it is bad. Reason for it is that his father used to beat him a lot in childhood. Quite a cliche idea, right? However, I base off it a whole plotline connected to this berserk state. Parental abuse can also be a source of unhealthy ambitions, which is the case for that character as well.
Other thing that I'd recommed is digging head into the typical horoscope descriptions. They provide quite a lot of useful information on personality sets.