It depends about what you want to write!
I just published my book, and I started writing it maybe three years ago with the theme of 'vampire' but as I grew up, my tastes changed and now the second and third books are much more grim.
Vampire books are superduper popular, but they are hard to sell, if you ever wanted to sell them. That's because the market is already full of Twilight, Vampire Academy and more -plus the market is dwindling.
Maybe you could have a girl who, unbeknownst to her, has been stripped of her title as heir to the throne, and her mother was taken in the ambush and her father was killed. Nearing the end of the story, your character meets her mother but does not know it. Her mother was taken as a fortune-teller for one of the new kings advisors, and your MC has the choice to kill her or not. Luckily, she spares her and finds out from the King (riiight before your character kills him) that the fortune teller/seer/whatever is your MC's mother.
I claim 0 rights to this, so you can adapt it or change it.