There are both a few similarities and differences between Tony's poor decisions in West Side Story and Romeo's in Romeo and Juliet.
One bad decision Tony makes is to go to the dance with the Jets, even though he no longer believes in being a Jet. In Act 1, Scene 2, Tony tells his best friend Riff that he has absolutely "had it" with gang violence and other gang-related mischief. Riff persuades him to go though because the Jets need Tony's help in stopping the Sharks. While Tony's decision leads to meeting Maria, flirting with Maria at the dance provokes her brother Bernardo, which ultimately leads to the rumble.
Similarly, Romeo makes an equally poor decision in agreeing to join his friends in crashing the ball the Capulet's are giving. While Romeo likewise meets Juliet at the ball, Romeo's presence infuriates Tybalt, which ultimately leads to both Tybalt's and Romeo's death.
One difference between Tony's and Romeo's decisions is that Tony was given enough time and opportunity to break up the rumble, while Romeo was not given any time to break up Tybalt's fight with Mercutio. Tony had planned to avoid the rumble, thinking that making it a fair fist fight was enough to solve the problem. However, he allowed himself to be persuaded by Maria into attempting to break up the rumble. Instead of trying to break it up himself, he should have had enough wisdom to report the plan of the rumble to the authorities. Hence, Tony's second bad decision was allowing himself to be persuaded to break up the fight and thinking that he could.
However, both Tony and Romeo made the same poor decision of killing for revenge. Tony foolishly decided to kill Bernardo after he had killed Riff. Likewise, Romeo foolishly decided to kill Tybalt after he had killed Mercutio.
Finally, one difference between Romeo's and Tony's poor decisions relates to Romeo's character. Romeo is far less practical than Tony is. Instead, Romeo refuses to be counseled by his friends, is a romantic dreamer, and much more inclined to wallow in self-pity than Tony is. Therefore another poor decision of Romeo's that is different from any of Tony's decisions is that he refuses to listen to either Benvolio's or Mercutio's advise to stop pining over Rosaline. In the opening scene, Benvolio urges Romeo to "forget to think of her." Likewise, Mercutio advises him, "If love be rough with you, be rough with love; / Prick love for pricking, and you will beat love down" (Act 1, Scene 4).