A couple of techniques I use are:
1 - Actual Events
Actual events are a good starting point. Sometimes things happen in real life that are so 'perfect', they'd be totally unbelievable in fiction.
eg:
a. When the leader of the Sherlock Holmes fan club is murdered under mysterious circumstances, the remaining fan-club members band together to use their idol's techniques to solve the bizarre murder. --- True Story ---
(OK, in reality they never solved the murder, but it's still a great starting point for a story)
b. In Nazi Germany, an enthusiastic member of the Hitler Youth discovers that he has an identical twin brother he has never met - who is Jewish.
This second one is really weird - totally unbelievable in fiction. If it wasn't true then I'd dismiss it as being too far out.
2 - 'What If ...'
Even with more prosaic real life events, you can always add the 'What If' factor. For example:
Prosaic reality. You are cleaning the basement ... but 'What If' ....
... What if you found a pile of old photos - you on the baseball team at school, university graduation photos, wedding photos, kid's first birthday ... but none of it ever happened? In reality you are single, alone, never graduated - never did any of those things in the photos, but here is proof of a life you don't remember having??? What would you do?
OK - this is what Derek would call a 'brain fart', but is shows how a boring event can be changed into the idea of a story....
Mac