What Shall My Story be About?

Animal and high school fiction is very popular. It all depends on the kind of audience you are looking to engage. Fanfics are easy to write and can be for a wide range of audiences. The most popular are: Percy Jackson, Divergent and Warriors, so you could start from there. You need to contrast the characters, add love interest, and make your books realistic, but unrealistic. For example, HP is about an ordinary boy who is a wizard, and the Hunger Games is about an ordinary girl See More▼ who is in a life threatening situation.
Here are some helpful websites:
http://writeforkids.org/2014/02/understanding-childrens-book-genres/
http://m.wikihow.com/Write-a-Tragedy
http://www.novel-writing-help.com/creating-fictional-characters.html
http://www.betterstorytelling.net/thebasics/identification.html
http://www.creative-writing-now.com/short-story-ideas.html

I think you should start with a college scene, but bring into a horror scene. You could do zombies, or murder killers. Anything really, because my favorite books are the ones that start peaceful and then it is all like BA BAM! Plot twist! Make sure to contrast the characters and maybe some romance.

High school and realistic fiction is very popular. My only concern is that they dwell a lot on stereotypes, infatuation, and overly tortured teens who come across as whiny. If you go in that direction make sure it's grounded in reality. Sorry I didn't give you any real ideas... :(

It can be a high school story. People tend to like and read those! :)