Sometimes you need to come up with a character in a pinch, and luckily, it's not too hard. Improvisers do it all the time, and they usually do it with little to no starting information. In any given gaming session, you have a wealth of context to work with; setting, genre, other characters, even the game rules and available character archetypes can help inform your characters. Should be simple, right?
Like many things in life, improvisational theatre has rules; "yes, and..." is one them. Others include: don't ask questions, don't have arguments, no transaction scenes, etc. These rules exist to guide players into creating engaging scenes on stage, by helping them avoid the traps and pitfalls that can cause a scene to falter. By that same token, roleplaying games have rules, giving concrete instructions for resolving conflicts, so as to prevent a game of Dungeons and Dragons from devolving into a game of Cowboys and Indians ("I shot you!" "No, you didn't!" "Yes, I did!").
I am an improviser. That is, I perform improvised comedy on a stage about once a week. I still consider myself to be a novice, but I've been studying the art for two years and it's been one of the best things I've ever done. The skills that I've learned from improv have applied to every aspect of my life, and this definitely includes gaming. Wingin' It will be a series of articles that touch on improvisation skills and how those skills can help make gaming run more smoothly, for both players and gamemasters.