Here's an excerpt from the former link:
I have entered the New Yorker's cartoon caption contest almost weekly virtually since it began, and have never even been a finalist. Mark Twain advised: "Write without pay until somebody offers to pay you. If nobody offers within three years, sawing wood is what you were intended for." I have done more writing for free for the New Yorker in the last five years than for anybody in the previous 40 years.
For the current contest, look here. And for more from me, look here.