From the story of Romeo and Juliet, explain the rules of marriage during their time.
Some additional rules having to do with marriage might have to do with the arrangement of the marriage.
Throughout the storyline Paris models this.
Paris, of noble birth, would be a great catch for the Capulets. Furthermore, he is interested in Juliet. One rule might be that an interested male much ask permission of the female's father. He does this in the first Act. Capulet tells Paris that he must win Juliet's heart. This seems counter-cultural to the possible marriage rules of the time. Yet, it just might have been that some parents in considering arranging the marriages of their children might have allowed love into the equation.
Later, we see Capulet rescind this quest for love and in haste and against Juliet's will begins the arranging of her marriage with Paris. This begs the question whether marriages were regularly arranged based on a whim or moment of intense emotion. That emotion would just be contrary to the emotion people generally use today.
The main rule of marriage that is relevant here is that young people in those days were not typically allowed to pick their own spouses. This was more true as one got higher up in society. In the society of Verona, the Montagues and the Capulets are high up. So Juliet would never have been allowed to choose her own husband.
Instead, her father would be expected to pick a husband for her. He would pick her a husband who would be good for the Capulet fortunes, either in terms of money or status. He would pick someone, for example, who owned a business that traded with the Montagues. Or someone whose family was connected to powerful people.
Marriages were about increasing family power, not about love.