Over the years I've made a few guidelines for myself in my writing. These are as much aspirational as practical (I am sure that any one of my plays has violations aplenty in its pages), but they've steered me well.

Passover

Each of my plays is an attempt to answer "What makes this night different from all other nights?"  If the situation is not different today from what it was yesterday, then there's no opportunity for change (which is what all dramatic narratives should be about).

But it's not just the overall narrative that this applies to. I also apply it to every scene and every line in every scene (including stage directions).  Everything in the script should be premised on evolving the mystery at the heart of the Passover question, and that can only happen if the "normal" suddenly isn't.

Give actors interesting stuff to do

The play, the thing on the page, is not, for me at least, only about my "message" -- as Sam Goldwyn allegedly said, "If you want to send a message, use Western Union." It's also about giving actors something interesting to do while on the stage -- to provoke them to move and speak in ways that prompt discovery and trigger surprise.  If they're interested in what they're doing, the audience will be interested in what they're doing -- and the gaggle of interested actors becomes my "Western Union."

"What if..."

I dislike it when a dramatic piece announces that it is "based on" or "inspired by" a true story -- too often, that declaration becomes the end-point rather than the starting-point of the endeavor, and all this effort is made to keep faithful to the original, often with a dulling result.

Much better to apply "what if..." to everything in a script in order to generate new possibilities for the dramatic narrative, regardless of fidelity to sources, as well as to unbuckle the narrative strait-jacket that writers get themselves tangled in as they work to "get their message across."

"What if..." is a solvent and provocateur -- use it liberally.

Comedy isn't jokes

I can't write funny lines -- I envy people who can, like Paul Rudnick, whose "Shouts & Murmurs" pieces in the New Yorker make me laugh out loud without effort, or David Sedaris in his less self-involved efforts.  But comedy in a play doesn't really come from the funny lines -- it rises out of the human situation into which the writer has embedded the characters and from which they struggle to extract meaning.  Detailed observation combined with the right amount of irony and skepticism will always evoke humor.  Which leads to....

Take it seriously

A play of mine recently done, The Greed Gene, has as its premise an absurdly exact rendition of genetic traits that an expectant couple can look forward to in their coming child: "an Eddie Bauer tendency along the sixth chromosome," for example.  But the play works only if it is directed to be completely serious in everything that goes on, that the world of the play, absurd to us, is completely natural to the characters.  The play is meant to satirize, but the satire will only work if there is no "nudge nudge wink wink" going on.  Too many plays that mean to satirize or condemn or sermonize about don't work because the writer wants the audience in on the joke or the condemnation, such as a play I recently saw that had several fundamentalist Christian characters. They were treated shabbily by the playwright because he wanted the audience to laugh with him about their "benighted" condition, but such a point of view breaks faith with the purpose of dramatic writing, which should to explore deeply the notion that nothing human is alien.

Never use "I remember" or monologue or phone conversations

Weak tactics to get across exposition -- dramatically inert, a form of cheating, a species of laziness.

Do the desk time

Every day, I keep my writing appointment, even if it's only to produce crap that I'll delete later. If one doesn't do the desk time, nothing valuable ever gets produced.

That's about it.