If you glance at the book's epigraph, you'll actually see that the title of Lucky Jim comes from the lyrics of what Kingsley Amis refers to as an "Old Song" entitled "Lucky Jim." Fancy that. The title seems kind of inappropriate at first, since for most of this book, Jim Dixon has some of the worst luck in the world.
At the end of the book, though, Jim's luck changes. Through no effort of his own, the world just seems to drop some very good luck on him. Mr. Gore-Urquhart decides that he likes Jim's whole tell-it-like-it-is style. In addition to that, Christine decides to break up with Bertrand and tells Jim she'd like to give him a chance.
Luck is what Jim decides completely determines one's lot in life.
It was luck you needed all along; with just a little more luck he'd have been able to switch his life on to a momentarily adjoining track, a track destined to swing aside at once away from his own. (19.140)
So in other words, don't read this book if you're looking for a lesson in morality, or proof that hard work is the key to success. If anything, Jim does everything he can to mess up his life, but gets lucky in the end. Pretty fatalistic view of the world, right?