I got this name, Josh Moskowitz and I think he should be happy that he got a full, good, easy to read name. I think in the book his friends will call him "Mos", but I'm not sure yet.
I think Josh will be a good main character that helps me when the other story I'm working on becomes too dark. In my mind's eye, I can't see a "Josh" being overly evil. Having said that, if your name is Josh I already am wary of you... sometimes you just can't win.
But while I have a main character, I don't have a story ready for him. One will come and I hope it comes just as I'm ending the Chess Piece Murder series, but I wouldn't count on it. I think it's valid to argue that the next topic to write about is also what I am interested in reading.
It has been said many times, "Write what you know", but I have to be honest and say I hate that phrase. It can take years to really know something, and by then you might not feel like writing about it. I think it's better to say, "Write what you believe". I can write about a chase scene in a small Italian village, having never been there or even looked at a map. I can believe that I turn the corner into a row of shops with a street filled with tourists, even if the street doesn't exist.
If the story becomes a huge hit, there will be fans who visit that village, and remark how there is no such street... but it doesn't degrade the story or the importance of that chase scene. So write what you believe...
As you may have noticed, I like to write in different genres. I seem to have something to say in a number of different formats. I like to write what I feel passionate about. And that's the secret to finding the next topic, find your passion. If you want to read it, maybe you want to write it. I say maybe because if this is your first fantasy book read, and now you want to write about a magical ring that needs to be returned to a volcano and destroyed... you might want to read in that genre a bit more.
Let's add to our motivation phrase, "Learn whats written". If you read Lord of the Rings, and now you want to write fantasy stories, I'm right there with you. So now look at whats #2 on the list, and on down to #10 on Amazon's list of fantasy books. See what sells, read what sells, learn the format based on what has been written previously.
To pick your next topic, look at your bookstand... and then inward for your passion.