Let's say that a big, reputable publisher (as in a branch of one of the big five) wants to publish a first-time author's manuscript. What rights are most important for a first time author to retain?

Over the years I’ve found that many aspiring and first-time authors are concerned about rights—which ones to retain, which ones to offer, etc.

Typically, publishers will want to purchase North American rights, although sometimes they will want world rights. If you plan to sell lots of foreign rights to your books, you might retain world rights and just sell North American rights; but if you don’t plan to pursue foreign rights, then allowing your publisher world rights might get you more money up front and maybe down the line.

If you’re writing a novel, film rights are good to retain.

Other than that, publishers will typically ask for all the rights to everything in the known universe and for all-time and for every conceivable type of technology in existence or that will ever exist. And no, I’m not kidding.

Your agent can help you navigate through all of that, but honestly, you’re a writer so my view is: sell the stinking rights, make some money, then write something else, sell that, and make some more money. However, don’t be stupid: read over your contract (something I’ve not always done carefully enough, much to my later chagrin), and then just know that publishers will try to get the biggest bang for their buck and your agent is your advocate to make sure you don’t get screwed over.

Celebrate the offer, sell the book, then sit down and start writing again.