Need an idea to begin with? 

Why not try out a writing prompt... 

What if no one needed to sleep anymore?  How would this change the world? (NEW) 

Begin a story with: "A tooth fell out." (NEW) 

What if you were changed into the proverbial 'fly on the wall'?  What meeting / conversation / event would you want to observe? 

What if you could talk to yourself in the mirror -- for real?

What if you woke up one morning and discovered you lost one of your five senses?

What if you woke up one morning and discovered you could FLY?

What if a loved one died?  How would this change your life?

What is one of the most traumatic incidents in your life?  Why?  How did it change you?  What if it happened to an entirely different person - how would they react? 

Name some anxieties or fears that you have.  Why do they cause you distress?  What kind of events would trigger stress related to these anxieties?  What if you had to face the source of your anxiety all too often?  What would you (or the character) do to deal with the situation?  (NEW) 

You are walking in a forest and discover a very deep, dark cave.  What's in there?  Are you going to go in and find out?

You see someone or something really funny or strange on the way to the store.  What is it?  How does it change the course of events?

The main character has an obsession with something.  What?  How do they fit their life around it?

Your main character is in love.  I mean head over heals, can't eat / can't sleep in love.  Suddenly he/she gets dumped out of the blue.  How does the break up occur?  What is the reason given?  How does your main character deal with his/her feelings?

Start a story with:  "Everyone called her/him/it crazy, because...." 

Start a story with:  "I love to eat..."

Start a story with:  "No one likes..."

Start a story with:  "I get angry when..."

Start at story with:  "Why can't I..."

Start at story with:  "I lost my job today.  I used to be a..."

I'll keep updating the list as new ideas come to mind.