Unless you get a bolt from the blue while you are writing your novel, a title is best affixed when you finish the first draft. Sometimes it takes a long while to match the right title to a book, and sometimes the marketing savvy of your editor/publisher helps fix the title. Here are some ideas on how not to put together a bad title. Once you have a potential title or titles in mind:
Check it on Amazon, B&N, or any other book seller site. You want your title to be nearly or absolutely unique. This means no one else has used it in common practice or knowledge. If you have a great title, but everyone and his brother is using it already, how will you separate yourself from the crowd? Just take a look at some common titles on Amazon and see how many hits they generate--sometimes thousands. If your title gets confused with a thousand other titles, no one will find your book. On the other hand, if your book has a strange title, you might get no hits at all.
Make sure your title reflects your work. Roz Young recommended my book Aegypt www.AegyptNovel.com be called, In the Tomb of the Goddess of Darkness and Light. That's catchy, but too long. There are some other works with Aegypt in the title and another work named Aegypt. Just one. I felt that that was great probability. Someone looking for Aegypt (either novel) would find mine. This is a positive.
Don't hold on to your working title if it doesn't work. For example, I gave a working title of Seeds for The Seeds of Rebellion to the work The End of Honor www.TheEndofHonor.com. The working title of The Fox's Honor www.TheFoxsHonor.com was Duel. The title of A Season of Honor www.ASeasonofHonor.com was Desert. These titles simply stood in place for the final titles. Eventually, the Honor theme became the focus of each of the titles, and finally, I gave the series the title The Chronicles of the Dragon and the Fox www.DragonandFox.com. This was a request from my publisher and made sense from the context of the books.
So to recap, make sure you have a somewhat unique title, that can't be confused with too many works. Check it out before you go to print.