I understand that Chris Baty (founder of NaNoWriMo) wrote a book called No Plot, No Problem. And since you’re writing 50,000 words in a month, maybe you don’t need a plot to start with and instead you’ll back into one. But as Edna Mode says, “I find luck favors the prepared, darling.” Below are a few links about plot and storytelling in general to give you a little preparation, if you so choose.
Pixar’s 22 Rules of Storytelling
Kirsten Bakis’s Nine Exercises #4: A Plot
Kirsten Bakis’s Nine Exercises #3: An Ending, and a Letter
Springhole.net’s various plot generators