I approach Characters from the POV of "What is their purpose?" Then I decide how to make them unique, starting with something that forms the core -- apperance, personality, name -- something that I can build a character around
Example: For a Fanfic based on the anime series
Bubblegum Crisis, a cyberpunk-style series. A trio of police officers are visiting a underground contact for data on a vigilante. The contact is a gang leader by the name of Skeeter Karns. So how to make him stand out?
First, I made Karns a giant -- large man, powerfully built. Then I decided that this guy had an IQ of 180. So he's smart and strong. But how to make him stand out even more?
I decided that Karns was an orphen that had seen the dark side of the city and decided to do something about it, but in his own way. He became a powerful gang leader who rules a large district. But unlike most gang leaders, he doesn't terrorize the district. In fact, he acts more like a benovolent dictator. He helps the people, puts kids back into school and encourages them to go on to college, establishes clinics and helps the orphanage whenever he can. The police leave him alone because his area is one of the few places where crime is not out of control
That doesn't mean he's all goodness and light. His gang is heavily armed and defend their turf from other gangs fircely. Illegal drugs are kept out, the pushers who try to work on Karns turf don't live long enough to realize their mistake. It's mentioned that a triad tried to run drugs through Karns territory, then tried to kill Karns. The result was that Karns gang wiped out the triad in question.
So, on the one hand, I have a character who was trying to do good, but on the other, was not someone you wanted to cross or have angry at you. Great.
But something happened. For some reason, Karns managed to insert himself into the story that occures before the one I had created him for. (I was writing three stories in the series at the same time, going from one to another when I had writer's block) Not only that, but he became an inportant part of the story line. A throw away line about him in the second story became the basis for an entire chapter in the first story that expanded on the people around Karns and why they were so sucessful. In short, he went from minor character to major on the strenght of his character.
Scary, no?
Craig