Read. Read lots. Read widely. And write.

Okay, suppose I've done that and I'm sure I've got something that will rise to the top of the hundreds, or even thousands, of other manuscript in a publisher's slush pile?

If you're sure you're ready for the heartbreak of rejection, there are lots of lists of publishers available and guidelines for submitting to them. You might start with Places for Writers. But be prepared for the fact that it takes a lot of patience and persistence - both to polish one's craft and to find an audience for one's work.