An easy way to create character choices in improv is to realize your character, much like yourself, is always coming from somewhere, and after this scene will be going somewhere else. This is not to say you should create in your mind a comprehensive character history for whatever character you happen to be playing. But it helps to come in with an idea of what has led your character to this place in time, with the other character(s) in your scene.
Is your character in the middle of a shitty day? Having a great day? Perhaps your character spent all day preparing for this moment, the scene you’re in right now. Perhaps your character has dreaded this moment. Perhaps your character has been enjoying the journey of the last day, week, month, year, life… or loathing it.
Perhaps your character has a long work day ahead, and isn’t looking forward to it. Perhaps your character can’t wait to get the hell out of there. Perhaps your character never wants this moment to end, or whatever happens next is nothing to this character unless they get what they want in this moment.
Imagine for a split second where this character is coming from, or where they plan to go next. From there, put yourself emotionally in that character’s shoes and imagine for a split second how you’d feel in that situation, where your head would be at.
Give it no more than a split second’s thought. You are in the middle of a scene, after all!
Take whatever sense memory you can glean from that idea into this scene, and play with that from here.
It could be the bit of information you need to help drive your improv in the scene.