Keep it moving.
Tell, don't ask.

A good player moves the scene forward and does not rely on someone else
to do it for him.  In a team of veteran improv players and novices, the
new players might be inclined to sit back and watch the veterans guide
the scene.  All of the players must believe in themselves and contribute
new ideas for a scene to be of exceptional caliber.  In this example,
consider the role of Mel:

    JEFF:  Oh my gosh that thing is big!
    MEL:  Yeah!  It's really huge!
    JEFF:  It's getting bigger!
    MEL:  It sure is!
    JEFF:  My goodness, it's eating the dog!
    MEL:  The poor dog.

Mel has accepted all of Jeff's ideas (she did not block), but has
done nothing for the scene itself.  Improv is about sharing, and it is
everyone's shared responsibility to push the scene forward.  What Mel
did in this example (i.e., accepting an idea, but not adding to it),
is often referred to as "wimping."

The most common form of wimping is asking questions.  Watch how Perry
accepts all of George's ideas, but then wimps by simply asking questions
instead of contributing new ideas.

    GEORGE:  Look at the new dog I got.
    PERRY:  What breed is it?
    GEORGE:  It's a German Shepherd.  IT can protect me against people.
    PERRY:  Who do you need protection from?
    GEORGE:  The Mafia.  They're out to get me.
    PERRY:  Why?

In this scene, Perry forced George to create all the ideas.  Improv works
far better when the workload is shared.

    GEORGE:  Look at the new dog I got.
    PERRY:  Wow!  A German Shepherd.  You must need protection.
    GEORGE:  Yeah, the Mafia is after me.
    PERRY:  I told you not to date that girl.

The scene becomes faster and more exciting.  Both players are working
together to create an interesting scene.  Eliminating questions and
redundant statements allows improv teams to pack more material into
their scenes.

Sometimes there are instances when neither player is willing to advance
the scene - a double wimp, often called "waffling."  Waffling occurs
because both players are afraid to take responsibility.  Many novice
players are concerned, "What if the scene does not work out?  It will
be my fault." Worrying about success is a dangerous way of thinking in
improv.  While it is true that a scene might not work, lack of certainty
is one of the things that makes improv so exciting!  Players who believe
that wimping and waffling will prevent them from embarrassing themselves
discover that their scenes will never be interesting.

Wimping and waffling are common at the beginning of scenes.  Instead of
jumping in and starting something, players wait and delay.  The following
is an example of a worst-case scenario of waffling:

    HARRY:  Hi
    JILL:  Hello, there.
    HARRY: So whatcha doing?
    JILL:  Nothing much.  You?
    HARRY:  I don't know.