I am sure that had I been Romeo or Juliet, I would have fallen for the other. They are 'star-cross'd' lovers after all, and they are fated to be together in love and death. I can (dimly) remember the passion of being in my early teens and captivated by someone who was all the more attractive for seeming to love me too. Past loves, like Romeo's affection for Rosaline, only make the young man more desirable as he is unafraid to show passion: an attractive quality to the young and naive Juliet.
If Romeo and Juliet could have been as clear-headed as some of us feel they could have been, I doubt the relationship would ever have occured. For one thing, Romeo with a clear-head would have realized that other girls would be as appealing and Juliet would probably not have been worth the effort of overcoming parental disapproval. Look how quickly he go over Rosaline. For another thing, Juliet would have realized how quickly Romeo changed his affections, as he had just been in "love" with Rosaline. She would not have considered him a good risk.
I hope that I would, but that I would go about it differently than they did it. I would hope that I would still pursue a relationship, but not in secret. I would hope that I would have the courage to face the disapproval of my parents and her parents and show them that they are wrong.
It's sort of like being Gandhi -- you have to openly disobey authority and take the consequences if you truly want to cause change to occur.
If I were Romeo or Juliet, I would do exactly as they have done since I would be one or the other. Were I in the same situation as Romeo and Juliet and were I a male, I probably would also be stricken with the beauty of Juliet; her unattainability would also be enticing. Yet, I hope that the last disappointment in love would have taught me something, and I would go slower, heeding the words of Friar Lawrence.
On the other hand, were I in Juliet's place, I believe that caution would take more precedence throughout her actions. First of all, she is in no hurry to marry Paris, having promised her mother that she would "look to liking love" only. Her reluctance to kiss Romeo when he asks and her use of the religious metaphor of the pilgrim on their first meeting also suggest a more chaste girl than she becomes in Shakespeare's play. When Romeo swears his love, she bids him not to swear by the "inconstant moon," so her rushing into marriage with Romeo seems rather inconsistent with Shakespeare's characterization. Therefore, in the role of Juliet, I would not rush into the marriage; there is far too much to lose with the feud going on and with pressure from her parents to marry Paris.
Knowing what we know from the Prologue, I don't think I would still pursue a relationship with either Romeo or Juliet if I were the other. Personally, I have great respect for my parents and their opinions. If a person was totally off limits to me (as I think Romeo and Juliet assume at the end of Act I), I would not look for the ways to keep a relationship up with them, I would try to get over it and look elsewhere. However, I say this with a clear head today as a mature woman in her mid-thirties. When I was 22, I married a guy my parents certainly wouldn't have chosen for me.
This demonstrates the concept inherent in man that rebels while we are young. We act on emotion when we are young, and more on thought as we age. We see this clearly for both Romeo and Juliet as each decision they make (to kill themselves, to fake a death, to take someone else's life and to keep up a relationship) occurs from an emotional response to a situation.