Usually by falling face down on my bed and wondering why, why, WHY I chose to be in this insanely competitive, rip-your-heart-out-and-stomp-it-into-the-ground industry. Then I read the rejection letter or rejection email a thousand times, wincing as each negative comment is permanently branded onto my ego. Or, if it was a rejection phone call, I'll recount every word of said phone call to my husband until he's ready to plaster my mouth with duct tape.
Only then will I sit down at my computer and bring up the rejected sample chapters, or manuscript, or outline, and calculate how many hundreds of hours of work I put into it. And mull over the fact that it will most likely never see the light of day. Instead, it will sit on the hard drive of my computer. . .and there it will remain. . .and remain. . .and remain.
After that, I head straight to my bookshelves and my kitchen, in that order, and proceed to drown myself in Jane Eyre and pepperjack cheese. Or, if it was a particularly painful rejection, House of Mirth and Fudgicles. Have you ever tried Fudgicles? They really work.
(Note to all the aspiring writers out there: This post is not meant to dissuade you from the rewarding field of fiction writing. But if you can't handle rejection, you should seek an easier career. Like lumberjack. Or maybe ironworker.)