There are a number of ways Romeo and Juliet might have made their path to happiness more smooth. First of all, both could have acted more maturely and told their parents of their love for one another. Instead, they immediately choose to subvert their parents, assume the worst, and enlist others in their immature cause.
Romeo, for his part, could have come clean. He moons over the loss of Rosaline, is coerced into attending the ball incognito, and falls in love at first sight. Juliet, too, is far from blameless. She impetuously throws away her life and family in order to be with a crush she knows nothing about and to whom she is attracted merely be sight and a few polite words. When the love-struck young man appears unbidden at her balcony, she swoons and hopefully implores: "Deny thy father and refuse thy name. / Or if thou will not, be but sworn my love / And I'll no longer be a Capulet" (2.2.34-36).
The pair continue with their plan of subterfuge, endangering those whom they claim to love (Mercutio, the Nurse) and those whom they can manipulate (again, the Nurse, and the Friar). When their best-laid plans are thwarted, they take the melodramatic, insecure way "out."
Although many characters share culpability, it is ultimately Romeo and Juliet who stand in the way of their own happiness.
In the long run, they do not overcome the obstacles that stand in their way, of course. During this time period, it would be nearly impossible for Romeo and Juliet to be together due to their families' fued with each other. Despite their intense love and desire to be together, Romeo and Juliet, in the end, could not overcome the obstacles that the family fueds brought to them. They felt overwhelmed and helpless and had no hope to be together...the end result was that both of them died. They were together in death, which is ironic.