The Basic Mechanism of Acting
Everything you do when you are acting depends upon two things. The action that needs to be carried out, and the behaviour of the actor standing before you. For all the technical differences, this does not change from stage to screen. The basic mechanics, the simplest mechanism of the actor’s process does not need to change.
So what you do in every moment you are acting depends only on two things.
Having something achievable to do in the real world.
Listening to the other actor with all of your senses.
It’s as simple as attempting to get them to do what you want them to do, while paying attention to what they are currently doing, so that as they change, you can change your strategy with them.
Keeping it in line with the scene is simple enough – base what you want them to do on what your character wants the other character to do in the scene. But here’s the kicker – adapt it so you do not have to pretend you are part of the fictional world.
So, if your character wants the other character to lend them money, behave as if you want the other actor to do you a favour – or if the scene is much more like they feel entitled to borrow the money, behave as if you deserve the favour, and then check in with the other actor constantly and change your tactics to suit their current behaviour.
The basic activity of the actor is responding to what the other actor is doing in the real world on a moment to moment basis, with an achievable task in mind.
I understand that it sounds ridiculously simple, but it just works.