Creativity has to come from inside... Or you seek out inspiration in something that means alot to you.
Or challenge yourself to just pic a random topic (flick through an encyclopedia) then research it to build up a story.
Sometimes when I know I need the practice I literally open up a black page on Notepad/TextEdit and stare at it until I start writing. Like really make myself start. A story doesn't have to start at the beginning either.
What are you passionate about? Weed. Write the ultimate stoner story.
Go to tvtropes.org (or something like that) and browse common plot devices.
Like 'the journey', 'the coming of age story', 'the account', 'the contest/goal-oriented story' etc.
It's your story. It's your plot.
Even if it sounds shit to you it's better than asking other people to give it to you.
Throw what you have in your head out there and work with it. It might be a whole lot better than you think. When it comes to writing, don't dismiss anything immediately.
Also, if you read alot of books you';ll be familiar with common themes and devices authors use. Get reading- get inspired.
Good luck.
Inbox me with your draft so I can Beta it for you.
EDIT: DUH... One last tip:
this might help