A very senior creative at an agency I worked at once gave me a very useful piece of advice: when writing a script, don’t write the dialogue.
This makes sense for a few reasons:
First, if you don’t write the specifics, there much less to object to. If a client/CD/cleaning lady doesn’t have an exact turn of phrase to pick apart, he/she can just imagine the best dialogue for your scene and let the script go. For example, writing ‘She explains why she hasn’t got a car and they agree to meet later,’ will make your life a bit easier than:
Woman: I left my car keys in the anus of a forlorn giraffe.
Man: Literal bummer. Shall we get together at the apex of the vernal equinox?
Woman: That sounds like a really, really, really, really, really, good idea.
The first method is also easier to read out without getting all choppy and losing the flow.
Another reason why this is a good thing to do is that it leaves room for later development. Someone might say something good in casting, or the director might have a good suggestion. If your dialogue isn’t buttoned down then changing it won’t be a problem. You can’t have a client saying ‘But I prefer the way you had it before’ if there is no before. Also, according to Jonathan Glazer, the wiggle room is where the magic happens. If you pin everything down then there’s no room for the happy accidents that make good things great.
A third reason is that writing good dialogue is not easy, so you don’t want to get all bogged down doing it while you’re trying to get your script structure right. Have a go at the dialogue by all means, but you might want to leave it until later when you’ve properly sorted out what goes where.
A fourth reason is that you might have more important things to do. If you spend ages nutting out every little detail and your client/CD/cleaning lady bins the script, you’ve wasted a lot of time that you could have spent playing Red Dead Redemption or searching the less salubrious parts of the Worldwide Web. Or doing some other work.
By the way, none of the above applies to radio ads which need to be buttoned the fuck down before you go in. You can still have wiggle room, but very few actors/VOs like to be told to make shit up on the spot. And the same with headlines. Writing ‘Witty headline goes here’ very rarely works, and I’ve got the P45s to prove it.