Now you may find this hard to believe. Really hard to believe. But in my humble opinion, 90% of the plays I see and read today, (I see and read a lot of plays) whether they are short plays 10 - 20 minutes or full-length plays, 90% of all the plays can be cut at least 15% if not more. Even short plays. Yes, in a nut shell, most plays today need to be cut. And often, drastically.
Cutting dialogue and even whole scenes from your play is like giving birth. It can be painful, long and arduous, but then the cutting process is over, often, you will have a better play. But to be honest, it is really hard to do, because often, WE LIKE WHAT WE WRITE, and when WE LIKE WHAT WE WRITE, it is really hard to cut it, even if it doesn't serve your play or your creative intention.
So how do you know what serves your play?
Start with these two questions:
What is the story you are telling? (Write it out in 30 words or less.)
What do you want the audience to do after they see your play? (Again write it out.)
If you get clear on the story you are telling, clear on the core of your piece, you will easily see dialogue, and even whole scenes that don't serve your intention. I have read so many plays that are ALL OVER THE PLACE - yes, they are often clever, or funny, or heart-wrenching, but they are just TOO MUCH. (Like the Christopher Nolan Batman movies - come on Christopher just tell one story really well. Let's really do that Joker story!) Get clear on the core, on, as they say, the THROUGH-LINE of your story, and you will easily see what needs to be shredded.
Also if you get clear on what you want the audience to do after seeing your play, you will easily see what in your play is not leading towards that intention. Maybe you want the audience to stop being so self-centered, and become self-aware and more spiritual. Or maybe you want the audience to begin accepting others and to love more unconditionally. Or maybe you want them to start taking chances in their lives, but whatever it is, the clearer you are on what you want the audience to do, the easier it will be for you to CUT all that doesn't serve your creative intention.
When you start writing a new play, just let the creative juices fly. Knowing that you will be cutting a play drastically will let your creative imagination go wild which is what you want. Then get clear on the story and your audience intention and CUT CUT CUT.
Learning how to cut whole scenes and internal dialogue is, in my humble opinion, the most important skill you need to be a great playwright. CUT CUT CUT so that your play is concise, succinct, clear, focused and on point. You can always add stuff back in if you want, but dare to rip, shred, and CUT CUT CUT your play to uncover the amazing butterfly within.