Look at each other
The more time you spend looking at each other, the better your show will be.
Charlotte and Andy form the British duo Folie à Deux and teach about 2-person shows. You can tell from their shows that they love working with each other and fully accept each other on stage all the time.
This connection is of course formed offstage too and a great tip is to spend a significant part of your warmup doing an emotional check-in and time simply looking at each other.
Improv is working together, so it will make your show better, in every single way. Always.