Well, yes and no. Unless you're writing the next blockbuster of the century, one book does not a career make. One book is just the gun going off at the starter gate. If you want to do this for a living, you need to anticipate that you will be putting butt-in-chair over and over again to write more stories. And you hope that editors and readers keep buying said books.
So one of the purposes your initial book (and every book after that) has to serve is to sell the next one. You want your readers/editors turning that last page and thinking--OMG, must have the next one!
There are a few ways to go about doing this. It can depend on the genre you're writing and if you're doing single-title vs. a series or trilogy. But here are some strategies to close the deal on the next book before it's even written.
1. The writing must be so amazing you take the reader to another place.
This is number one no matter what. Great writing. Period. If this isn't there, you've already killed your chance for next time. This is why I caution people about jumping in and self-publishing their first novel. I look back at my first novel and cringe. Had I put that out there, my name would be attached to that level of writing. Ack! So keep in mind that ANYTHING you put out there with your name on it can either pump up or sully your reputation as a writer. Therefore, make sure you only put the best product out there.
2. Cliffhangers (but not shameless ones!)
This is a delicate balance. Cliffhangers are absolutely awesome for making your readers desperate to have the next book, but be really careful with this. A shameless, brutal cliffhanger also runs the risk of pissing off a reader. I have seriously stopped reading an author when I feel like I was taken for a ride then left hanging on the edge with no resolution at all. Each book has to have ITS OWN ARC. You have to tie up the main threads of the plot in that book while still leaving unanswered questions for the SERIES ARC. Those arcs are two different things. Do not twist up all that tension and then leave the reader in a knot. Give them some relief.
3. Main characters that are strong and interesting enough to keep readers coming back for more. (Series--same hero/heroine.)
If you are going to write a series that follows the same main characters, you have to create heroes and heroines that are knock-you-on-your-ass interesting. (And humor helps too. I find myself more drawn to ongoing characters who are funny/sarcastic and entertaining.) Following the same people for one book is a big enough commitment, so for me to follow those same people for another two, ten, fifteen books, they better be amazing. You have to create a character with so many layers that you can continue to peel back with each new story. For instance, the Sookie Stackhouse series by Charlaine Harris (True Blood). Those characters are so colorful and entertaining that you are happy to spend some more time with them.
4. Secondary characters that the reader falls in love with. (Series--different hero/heroine, same world.)
If you want to write a series, especially in romance, this is vital. For instance, my books are part of a series but each book is its own complete love story. Therefore, CRASH INTO YOU's story is about Brynn and Reid. Then MELT INTO YOU is going to be about Reid's best friend Jace, who was introduced in book one.
And I can tell you that without fail, every single person who has read my book so far has asked the same thing when they finish it--"When is Jace's story coming out???" And both my agent and editor told me early on--Jace's book has to be next. So apparently I've done a good job of setting up my secondary character. Readers were loving him and anticipating his story before the next book was even written. Another good example is Adrian in Richelle Mead's Vampire Academy series. He's such a likeable character that you want to know what happens to him. So now he's getting his own spinoff series.
5. A fantastic author voice.
This can get me every time. If I love the author's voice--the wit, the style of writing, the way they can put together language--I'm going to line up to buy whatever they write. This is why even though I don't read science fiction, I still picked up Lauren Dane's Undercover which takes place in space. I love her voice and her stories, so I'll follow her into genres I may normally not pick up. Same with Jo Davis. She's coming out with a shifter series (writing as J.D. Tyler), which I probably wouldn't have looked at twice if written by someone else, but I heart her voice, so I'm interested.
So when you look at THE ONE BOOK you're trying so hard to sell, try to find what is going to make someone want to buy your next book. Editors usually want to make multi-book deals, so give them a good reason to take a chance on you. :)
Now, you guys tell me, what hooks you into wanting to buy another book from that author? How do you feel about cliffhangers? And which authors/books have you read where you absolutely couldn't wait to get your hands on the next one (like you're on Amazon within ten minutes of finishing the book or your schlepping out to Barnes and Nobles in your pajama pants)?