Well, it's a good thing I just got out of a Theater History class!
Maybe you could try to think of the plot as a vehicle — a method of sorts to help move your characters about. Take it step by step; think about where a character starts, then have his/her (or another character's) actions or choices — especially
choices — move the character to the next stage. Taking cues from Romeo and Juliet
, the death of Tybalt (following Romeo's snap decision to avenge his friend)
in the big fight scene inspires the star-crossed lovers to take desperate measures. Juliet hatches a plan to fake her death, but when Romeo finds out he think's she's really dead, and thus kills himself, and...well, I think you know how this story ends. (Not well). The point is, maybe it might be useful to consider the plot in terms of reactions to actions.
Barring that, you can try sticking to the basic plot graph◊
you see all the time in English classes — simple, yes, but it rings true. Fill in the blanks at your leisure, and it's likely that you'll be able to come up with something.
Hope that helps you out, my troper comrade.