If you still need ideas do what I do to start one (if it's helpful to you that is. You might find other peoples ways easier I dont' know.)
1. Think about what type of genre you'd like it to be
2. Come up with the main character(s) names
3. Come up with extras- friends, family, teachers, etc.
4. Have a personality in mind for each
5. Think about what you want the story to be about (beginning middle end)
6. Basically write down what you want to happen
I hope that somewhat made sense and was helpful(: