Using what I learned while directing some of the best improvisers in Chicago for my feature debut as a writer/director, I would share the 5 pieces of advice I have for anyone looking to direct improvised moments on camera. In brief, they are:

1. Encourage your cast to try any change they want, unless it involves the plot.
2. Trust that your actors have probably surpassed you in terms of knowing these characters.
3. Feel free to chime in when necessary.
4. If nothing else, improvised takes can be great for morale.
5. If you know your actors’ strengths as improvisers, cater to those things.

Each of those would come with a paragraph that expands on the ideas and provides examples from my experience. In addition to writing and directing this film, I've also acted and improvised in front of the camera for several projects, and I trained and performed at all of the major Chicago improv theaters before that, so this is about as close as I get to being an expert in something.