You should write what you want and care about and not what you think you should write. It’s not about writing what you suppose is a big important subject, but what is in your heart and what you are passionate about. That could be a play about labour politics or a play about a cat.
I would read as many plays as you can lay your hands on to try and pick up the difference between writing at the speed of an actor’s thought and descriptive prose. It doesn’t matter whether you are writing realism or something non-naturalistic, all playwrights are writing at the speed of an actor’s thought.
Go to as much live performance as possible including theatre, dance, comedy, opera, and live art. This way you can begin to see what happens between an audience and a performance and how it works. You can only really begin to fully know how tension is wrought, a subtext grown, or a joke landed when you’re able to put yourself in the audience’s shoes. As David Hare says “the play is in the air”.
Reading plays and seeing live performance also helps you to develop a taste and to learn how to tell a story, through action, in an elastic, theatrical way.
Writing ‘The End’ doesn’t mean you have completed the draft or finished the play. You have just got to ‘The End’. Work on your play script until you can do no more.
While there are many people out there who will give you feedback this is not an excuse for not doing your job to the best of your ability. It is your play with your name on the front. Take pride in your work and do not give the play over or send it out lazily because you expect other people to do your job and make it better for you.
For the Royal Court: In Basildon, Incomplete and Random Acts of Kindness, Under the Blue Sky.
Other theatre includes: Market Boy (National Theatre), Under The Blue Sky (West End).