Levels of NPC Development

Give just enough detail

The level of development spent on an NPC should reflect the amount of time the players spend interacting with him or her. It's a waste to completely develop the random wanderer players meet on the road. It's equally wasteful to avoid detailing the background and traits of regular contacts and followers.

For those familiar with management theory, I tend to use the Pareto Principle when working on roleplaying games. This principle states that 80 percent of your results come from 20 percent of your effort.