Starting Point

The starting point for creating a plot is asking yourself "What Needs to Happen?"
Don't worry about answering this in detail right away. You just need to start with the basics. They don't even have to be in the right order.

Examples:
Character A needs to have a troubled life
Characters A, B, C, and D need to meet up
A certain item needs to be found
a face off with the bad guy has to take place
the bad guy has to die
Character D has to turn traitor
they have to discover this secret place

Once you've got the most basic skeleton of the plot, try approching it a little like a research paper. Make a paragraph for each of these important points and start adding some details. Again it doesn't mean it has to be written in stone, you might try making several pages with this plot skeleton, and then filling in alternative details under each one so that you can compare them.

Character A needs to have a troubled life. It is troubled by a cruel stepmother and forced labor. It ends when character A makes an impression on character E who takes A under his wing and away from home.

Characters A B C and D need to meet up. A meets B through E at the new place and C turns up there after a couple years. C sparks a journey on which they will later meet D.

and so on...