There's an awesome set of storm clouds churning over my house right now ... well, not directly over it, more to the southwest, but anyway... I went in my front yard and wanted to shoot some bracketed exposures during what little was left of the waning sunlight. The setting sun was hitting the clouds just right, giving them a firy, hellish glow.
Little did I realize that I made what is probably my most common mistake. I left my camera at 800 ISO when shooting these shots, and high ISO combined with low light means noise galore. There isn't much I can do about the noise in this photo without destroying what detail there is in the clouds.
Of course, by the time I realized, the moment had past and the light was gone. I had read this article by Scott Bourne a while ago, but I only half-followed the advice. Sure, when I knew I had an important trip or shoot the next day, I'd go through and reset everything. But for those spur-of-the-moment shots like tonight, I all-too-often have wonky ISO or exposure compensation, or worse -- have forgotten to put in the memory card!