One of my least favorite things when I was a young playwright was rewriting. I kept thinking that if I spent so much time and energy writing the play that the last thing that I wanted people to do is to start critiquing it. I think one of the biggest mistakes that playwrights can make (like I did) is thinking that once the rough draft is over that the play is finished. What you do is set yourself up for failure. You have so much fun writing the draft and it takes so much out of you to finish it that when you finally submit it and get it in front of people you're not ready for the kind of criticism it will receive. And then you start going through the self feeding cycle of: "They didn't get it! I'm a horrible writer, I should give up now!"
But look at it this way. Most of the time we're like fish out of water in our plays and don't know we're wet. When you put a play in front of other people who weren't there when you wrote it then they can see a lot of things and have a lot of question that you don't. One of the things that I have grown to love in my grad school is the Lab class or the festival reading or a myriad other classes where you get someone reading your play and then critique it later. At first I thought I would like the readings more because I thought it would stroke my ego to hear my plays read out loud and hearing people applaud. I actually found that I loved what could be described as the most humbling aspect of it. I loved sitting with a group of my friends and colleagues and tear apart the script to find out what needs to be clarified or fixed. It's fun to see the little nuggets that they found in the play that you never saw or questions that you never answered. These kind of things expand the horizons about what your play can be and how it can be better.
My biggest advice is to get your tribe together. Your tribe is a group of people who you trust with your work and trust you with theirs and are willing to devote themselves to this process of making your art better. That's the biggest lesson I learned in all of my grad career. That tribe that you build as you develop your work and help other people develop theirs is the greatest asset that you have as a playwright!