Be very, very clear with action lines. For example, in a hostage situation: “He presses the knife into Dave’s neck”. You’re thinking he’s threatening to kill Dave; I’m thinking Dave’s dead.
Keep your scene headings/sluglines under control. “INT. SPACIOUS BEDROOM - BOB’S HOUSE - THE EAST SIDE OF TOWN - AFTERNOON” is way too much. Try “INT. BOB’S BEDROOM - DAY”.
If you’re using the trope of repeating scenes in which your protagonist has disturbing nightmares that hint at the overall mystery, at least make the dream scenes reveal something new each time.
Sci-fi screenwriters are always naming their characters/planets/alien races after famous SF authors. Same with fantasy and horror. Please, no more “Lovecraft Institutes” or “Space Station Heinleins” — it’s a little distracting.
Rules are made to be broken. If it works — serves the character, advances the story, excites the reader — it’s right.
Don’t be unsure in your action lines, e.g. ‘The walls shake a bit’, ‘There are maybe two dozen people here’, ‘Paul frowns, perhaps wondering what Howard is talking about’. If you don’t know what’s going on, how is anyone else supposed to?
A script that only includes scenes with the protagonist present feels very different from one that cuts between separate groups of characters. Both styles are useful. A focused perspective gives drive, immersion, maybe claustrophobia; a larger scope suggests a bigger world.
When outlining, you need to know how it ends… but that doesn’t mean you have to know exactly what happens in Act Three. It means you have to know what mental and emotional state you want your protagonist to end up in.
Don’t describe your script as one thing and write it as another. Why call it a “psychological thriller” if it’s a gory slasher? Why describe it as “slow-burning noir” if it’s straight-up action?
No matter how long you take, no matter how detailed you make it, your outline will always be missing something. It’s usually something deep within the characters. You need an outline to write the script, but you need to write the script to figure out what the outline is missing.
Don’t just create a bunch of characters with dreams, flaws and noble urges. Create characters whose dreams, flaws and noble urges intersect and bring them into conflict with each other.
‘Origin pilots’ aren’t as effective as pilots that give a sense of what a typical episode should feel like. Don’t write the characters’ first meeting. Just jump in — write your pilot like it’s episode two, and fill in the details through clever use of dialogue.
Celebrity cameos do not actually add value to your spec script. (Unless you happen to know the celebrity personally — then they’re probably great!)
When writing a synopsis for yourself, feel free to make it as dry and boring as you want. It’s just a tool to help you write the script. But if you’re writing a synopsis for someone else, you need to tell the whole story in those few pages — emotion and all.
The relationship subplot doesn’t have to be about romantic love. Platonic friendship is just as powerful a narrative force. Look at MIDNIGHT RUN, or the classic example of Kirk and Spock.
The key to writing a good monologue is to give it an arc. No, really. A monologue that starts in one place and ends up in a very different place is interesting and revealing of character.
Coincidences and moments of disbelief suspension actually work better when you don’t call attention to them. Lines like “What are the odds we’d all get here at the same time?” will make the audience wonder: hang on, what are the odds?
Don’t sweat too much about people suggesting changes to your script. Think: what’s the one thing your story absolutely can’t live without — the vital element that holds the whole thing together? Fight for that; the rest is negotiable.
When first sketching out ideas for a TV show, don’t get hung up on the pilot. That’s a completely different problem. First, figure out how your whole show idea works on a macro level. Once you’ve got the formula, then apply it to the pilot.
If you find yourself writing ‘dead weight’ dialogue — the characters don’t sound like themselves, or they’re just speaking rote phrases so the plot can move forward — stop. Close the script and go back to your outline. You’ll most likely find your problem in there.