If one were to look back at the events that led to the tradegy and construct a how-not-to-do-it manual, what would you suggest? I would start off by perhaps with "Avoid Family Feuds" and pointing out how the actions they feel make them respected actually have the opposite effect. What else would you include?
I agree that the parenting would have to be changed. Juliet's parents are not in tune at all with their daughter. Her mother leaves everything to the nurse. Her father is only interested in her blind obedience. Teenagers are not prone to rote acceptance of their parent's commands.
Juliet's parents would have to deal with her in a different way, most likely having to compromise on their rigid family war.
That's a fascinating question, because it is so complex. These families have been at war as long as anyone can remember; how, then, could we get them to not have such feuds? They would be part of how they define themselves.
Where could we realistically intervene? Honestly, I'd say closer parenting. For all that Juliet has strict rules, she doesn't seem in much ongoing contact with her parents. There's little enough education going on. I'll leave morality out of this, because that's so complex, but even practicality or emotion seem unaddressed. Romeo isn't good at the violent intrigues. He could benefit from even a little Machiavelli.
I would also urge Juliet's mother to not give up so much of her mothering role to the Nurse, who proves to be a poor decision maker and guide for her charge. Perhaps if her mother wasn't so cold and distant, Juliet would have felt better coming to her personally for advice.
The Nurse and the Friar should never agree to be part of a plan that goes behind the backs of the parents. Both of these people have not only a responsibility to Romeo and to Juliet. They also have a responsibility to the parents of the couple. He should agree to go talk with the parents rather than marry them secretly. The Friar is totally irresponsible in his plan for Juliet to take the drug that makes her appear dead.