How to find the subtext of scripts
It’s a tricky one this because there are no hard and fast rules about where subtext may lie (if there is any!) and so mining a script for all it’s secrets can be a difficult process. But there are one or two things you can do to help, and to exercise that part of your brain to spot any subtext more easily in the future.
You need to familiarise yourself with the script you are working on as much as possible. Read it as many times as you can, and that doesn’t mean just four or five times, but ten, twenty, thirty times even, to the point where you even know what’s going to happen next and what the characters are going to say next. That way every little moment will start to bleed into your conscience, and, if it is a good script, bits of action or dialogue you thought may have been inconsequential previously, may now be very important to the character or illuminating to the audience.
In reading if for the second time, study what the characters are saying, but in terms of subtext, you will need to scrutinise what they are actually doing in the scene, why they are doing it, and then why they are choosing to say those sentences and those words to do what they want to do at that point in time. Write this down, and be specific, and you will start to see if the words they are saying jar or go with what their objectives are in the scene, and in the whole script. If they do seem to jar, or the dialogue seems to be passive when the situation feels like it has higher stakes, you may be on to something.
Also, good exercise you can do is to think of a film you have seen not that recently that you remember had a good amount of subtext in it. If you can’t think of one, 1940’s film noir is a good starting point as they were quite subtext heavy (Double Indemnity being a good example), but any high quality drama film will have it’s moments. Try to go for Oscar winning performances and/or screenplays. Get a copy of the screenplay (there are plenty of online screenplay websites and most are published), and do the above exercise on that script. Really scrutinise it as much as you can. Then watch the film and see what the actors do, and this will illuminate the work they have done and decisions they came to in their preparation for the film. Think about how it compares to what decisions you made, and if things are significantly different, try to work out why they might have come to the decision to go in that direction instead of what seemed right to you. This is very useful work, and if you have seen a performance you particularly admired, even a performance which seemed magical and unattainable to you; doing this work can confirm that it is possible for any actor to get to that point, because the actor on the screen read the script exactly the same as you, and created the performance you saw - and which moved you so much - out of it by doing their own hard work.