I usually choose an emotion that I want to associate a character with.
For instance, I based a 1e elf mage on the emotion of fear - his parents were killed by a dragon, and he was always afraid someone else that he cared about would be killed. So he studied magic so that, the next time someone he cared about was in danger, he could save them - or at least make an attempt to.
It's difficult to come up with new characters, because I don't like to replicate emotions. Sometimes, though, I use NiTessine's system - using a sentence or quick character concept, and then work on it from there.