Creating Memorable NPCs

Over on Reddit I saw a link to this article by Charlie Jane Anders.  Her article targets writers, and she offers ten tips for writing unforgettable supporting characters.  Non-player characters in role-playing games fill a similar niche to a work of fiction's supporting characters, so these ten tips should be applicable to creating NPCs as well.  I've been trying to get better at creating NPCs that stand out in the players' minds, with mixed results.  I like that this article gives me something tangible to focus on.

I have had a few successes in the past, but mostly my NPCs come out a little flat.  One in particular, though, stands out.  Rixin the pixie is the one NPC whose fate my adult gamer friends actually cared about.  In fact, when one of the PCs died, we decided to bring Rixin into the party so one of the players could run him as his own character.  

By blind luck, when creating Rixin I seem to have followed nine of the ten steps the article prescribes.  Take from that what you will.  I know I'm looking forward to trying it on purpose.