On his Improv Nerd blog, Jimmy Carrane posted an article about how to decide if you need to walk-on into a scene. I'm going to use it as a starting point for my students, and so I thought I'd share his tips with you here in their entirety (bold-italic emphasis is my own). Additional commentary, however, is shared below the tips, so keep reading.
This is usually easy to determine and can be of maximum service to the players in the scene. If two players come out and have no idea where they are after a few minutes, it is the perfect opportunity for a walk-on. Come in and place them in a specific environment, such as in a restaurant, in a hotel room, on an airplane – anywhere but “vagueland.” Then quietly leave the scene, because your job is done.
2. Is a character being called for?
Sometimes, two players will start a scene and they’ll reference another character, such as, “Your mother and I are really upset you didn’t come home last night.” We don’t have a mother in the scene, so this is your opportunity to be the mother. It doesn’t matter if a woman or a man plays the mother, we need a mother. You want to avoid where the players are desperately calling out for another character to join them three or four times before some one is brave enough to step up. I have also seen the opposite where players are trigger happy and think every time a character’s name is mentioned is an opportunity for a walk on. Be aware that is some cases they will be referring to character and a walk on is not necessary.
3. Does something need to be heightened?
This is by far the trickiest one to do. Ask yourself if there is a game, premise or emotion in a scene that needs to be heightened. Can you do it gracefully, by adding a piece of information that will up the stakes? If so, it might be time for a walk-on. However, remember that you don’t have to jump into every scene. Sometimes a scene may not need heightening by you; they may be able to handle it themselves.
4. What is my motive?
I am guilty of this. Sometimes my confidence is low and I feel safe walking into a scene than initiating one myself. If you feel you are doing this, instead of looking for an opportunity to walk into a scene, how about following the fear and starting a scene yourself?
5. Does the scene need an edit?
I wish I could take credit for this advice: “Sometimes your best walk-ons are edits.” This is true, especially if the scene has been going on for a while. If the scene feels like it’s dragging and you have an instinct to walk on to change the energy, probably it would work better as an edit.
1. Group Mind
How well does your troupe play together? Do they (or the players currently involved) sync well together on stage - and if so, does that make it more likely that they'll be able to get themselves out of a bind? Are the players that are planning to walk-on naturally in tune with what's going on in the scene, and in tune with the other players?
Are the players currently in the scene newbies or vets? If they're vets, it's more likely that they'll be able pull themselves out of a jam - or make it more apparent when they're explicitly calling for a walk-on. Watch and listen carefully for cues they're giving to their offstage scene partners.
Certain players will tend towards certain types of behaviors in scenes - use those tendencies to govern where you think the scene will go. Does a scene player always refer to a third character with the expectation of them suddenly walking-on? If so, there's your cue - let them endow you with that character, and walk-on when needed. Does a scene player start out really strong scenes, but tends to forget to clearly define their environment? Walk-on quickly, give them a bit of definition, and then move on your merry way.
Walk-ons can add so much to a scene - or seriously derail it, if not treated with care and respect. Work on it with your troupe - it can become a great tool in your improv arsenal.