(The conversation's been a bit on the deep end lately so I thought I'd throw one in for the occasional student who comes by looking for homework help.)
If you need help remembering the plot of Romeo and Juliet, study Friar Laurence's confession in the final scene. He pretty much tells you the entire play:
Romeo and Juliet got married in secret, but then Romeo ends up getting banished when Tybalt is murdered. Juliet's parents think she's upset about Tybalt when really she's upset about Romeo, and they arrange this hasty marriage to Paris. She comes to me saying that she'll kill herself if I don't do something, so I come up with a plan. I'll give her a sleeping potion that makes everyone think she's dead. Then I'll write to Romeo, informing him that she's not dead, and that he should come to the family tomb when she wakes up and take her away. But I discover that Romeo never received the letter! So I raced over to the tomb to rescue her myself, figuring that I'll come up with a new plan once I can straighten everything out. But then I see Romeo and Paris both dead. I try to get Juliet to leave with me but she won't go. I heard a noise that I went to explore, and when I came back, she'd killed herself. If you don't believe me ask her nurse, she knew all about their wedding. It's all my fault, I accept that, and throw myself on the mercy of the the law.
Between that speech and the opening prologue ("Two households...Verona....ancient grudge.....young lovers take their life....") you've got the idea. Now, I'm not a big fan of saying "There you go, just study that and you're all set." If you do, you will have missed all the poetry (not to mention the sex and violence) in the middle. Think of this speech more as a set of pegs on which to hang the rest of the details of the play more easily for yourself. Who did Romeo kill? Tybalt. Who gave Juliet the sleeping potion? Friar Laurence. Why did Romeo think Juliet was dead? He never got Friar Laurence's letter. And so on...
Hope it helps!