One of the hardest things for new parents to understand is not everyone loves a baby as much as they do. This is a lesson that we have to apply to our books and our writing. There are millions of readers, each with their own need, imagination and drive. A die hard fantasy fan probably isn't going to be interested in a love story--unless it occurs in outer space.
So if I were a fantasy writer or science fiction writer--I'd become a Trekkie and attend every conference I could find.
Young adult--I'd get in touch with my elementary schools and/or middle schools and do a program. Schools are always looking for someone who can encourage their students to read and write. No, you're not going to sell any books that day, but if those kids go home praising you, the next time they're in a bookstore, mommy and daddy are going to be buying your book. Make sure you have a nice flyer or brochure for every child to take home with them.
Mystery--lots of people love a good mystery. Start a who-dunit club and have contests. Tag into banking parties, local clubs, etcetera. Sell yourself and you'll sell your book.
As new authors we have to think outside of the box. Bookstores are not the only place people look for good reading material. And you don't always find the ones who would be interested in your 'baby'. Do an honest appraisal of your book and ask youself, "who would most enjoy reading this?" And be honest, just as every parent must be honest. Not everyone is going to love what you've written. Once you've actually scoped out your market, figure out how to best reach those people. People who love to eat, sometimes are the same people who love to read. Carry brochures with you and every time you stop to eat at a restaurant ask if you can leave a few in the waiting area. Rest areas are another good place to leave reading material. Airports. Never pass up an opportunity to promote yourself. Oh, but do ask before you just toss something in a waiting area. There's usually a place for those things, and if you just leave it lying around chances are it's going in the trash, and the person that has to pick it up won't like you or your work.