Above all, remember that a poem isn't necessarily any good if it's rejected. 99 times out of a hundred, a rejection simply means that you and the editor who rejected the poem have different tastes. When that happens, submit the rejected poem to a different publication and editor. The same thing is true with short stories, too. Besides, that's why there are so many publications out there.
Different people have different tastes.
So, keep on submitting and sooner or later, you'll probably sell most of what you've written.