1. Focus on Relationship!
Too many improv scenes fall into an all-too-familiar pattern: two characters talking about what they are doing. But the fact is, it isn't interesting to see two miners talking about mining. It is definitely interesting, however, to see two miners talking about what they're going to do with all the money they get when they strike it rich. Maybe they even want to move in together! Maybe one of them is going to start a mining museum. Maybe one of them is going to go on adventure to find his long lost love.
2. Know Each Other!
One of the most common mistakes I made when I was just starting out improvising was starting a scene where the two characters didn't know each other. Maybe I was ordering a hamburger at the new restaurant, or maybe I was asking for assistance with directions from a stranger at a subway station. I eventually stopped doing these because they weren't working, but I never understood why until recently. When the characters are just meeting each other, there's no room to explore the depth of the relationship! However, when the other character is a best friend or a significant other, you can share your most personal feelings with them. The relationship can evolve and develop, and the audience gets to see what life is like for these two characters.
3. Agree with Each Other!
An improv scene can't go anywhere if the characters can't even agree on the basic terms of the scene! This way, instead of arguing about what to do, you can progress in the scene. And more importantly, the audience will be impressed because you're doing it together!
Another way to agree is called matching. This is where you match the other character's personality, mimicking their voice, quirks, and posture. Even if two characters don't know each other, they can have a ton in common if they match each other!
4. Play A Character!
It's very, very easy to play yourself in an improv scene, but it isn't particularly interesting to do so. It's more fun to be someone who has aspirations or quirks that the audience can catch on to. You can make a character a thousand times more interesting with something very subtle, like an affinity for plants. Plus, that kind of stuff can come back later in the show, and the audience will love it because they'll be reminded of that character; they'll get to know the character on a much more personal level.
5. Play with Patterns!
The funniest joke in the world can't draw as many laughs as a well-played pattern. When you call something back from earlier in a scene or a show, it's way funnier because you remembered it. It doesn't even have to be something funny; bringing something back a second time shows that you're paying attention, and the audience will think it's great because they remember it too.
6. Edit! Edit! Edit!
I think more than half of all the improv scenes I've ever done should have been edited sooner. Particularly in Easily Amused, I was not even aware that there was a technique to editing. I thought that a scene ended when everyone in it found an excuse to leave the stage.
In reality, a scene should end after its peak. Sometimes the peak is a resolution to conflict; sometimes the peak is a hilarious callback to something that happened earlier. And sometimes the peak is the escalation of a pattern to its natural resolution. For example, DeBono once had a piece which involved my character (a mailman) being bribed first by a golden mail bag, then a platinum UPS truck, then a diamond mail spaceship. And then the edit came because that was the highest possible escalation of the pattern!
In long form improv especially, edits should come sooner as a piece goes on. The scenes should get shorter and shorter, reaching their peaks sooner, to enhance the natural rhythm of the piece.
These are all things I wish someone had told me; so I hope I can tell somebody who needs to know this stuff!