Have あなた ever heard of the game Exquisite Corpse? If あなた don't, it's really simple. Just open a dictionary and flip through the pages quickly, stop, then use the first word あなた see または your finger lands on. Then do it again until あなた have another word (ex: helpful igloo) and write a story about it. That's what I do when I'm blanking on ideas.
I can't really help much, since stories should come from yourself. If someone hands あなた an idea on a silver platter, it is hard to make it your own and 愛 it. On the other hand, I know it's difficult to think up a good storyline. It always seems when I want a story idea, they run away, and when I want to keep focus on one story, I am flooded with inspiration.
That is the point. I think that ideas know when あなた are looking for them, and they want to play hide a seek with you. I would suggest leaving it for a while, and not focus your whole attention on finding the right story idea. (Although, あなた should always be ready with a paper and pen just in case an ingenious idea hits you.) But あなた can still always try game like the person above me described. That always helps too!
Just know that inspiration if everywhere. I literally thought up an idea for a story while I was looking for my shoes.