I think the single biggest obstacle for beginning improvisers is fear. Fear that they won’t make the right choice, fear that they won’t make a choice, fear of playing with people more experienced than they are, fear that they won’t remember all the stuff they learned about improv.
Mick Napier, in his book, “Improvise: Scene from the inside out” (my favorite improv book) says, “Fuck your fear.” Succumbing to fear on stage leads to safe, boring, vanilla choices. This is stuff the audience can see in their office at work, choices that are socially acceptable and that everybody makes everyday.
The audience wants to see things that happen the day the shit hits the fan, the day that someone has an emotional revelation that changes everything, they want to see the tension and excitement and danger of what happens when people make bold choices. The solution is to do something, to do anything, anything at all, as your character, and see where it goes. You’ve gotta give your character something, anything, anything at all, at the top of the scene, not doing so is a choice based out of fear, not doing so forces you to rest on your laurels and be jokey, grabbing for the moon’s reflection in the water like a monkey. The simpler something you give yourself the better, because you’ll be able to expand on it based on what the scene calls for as it builds and heightens organically.
The audience, and your team, aren’t interested in your fear. They’re interested in seeing your power. The more you leap without having a net, the more fun you will have and the better your show will be. When you fold to fear, you’re telling the audience to fuck off.