As humans, we're born with lots of instincts that are shamed out of us as we get older. One of the most important experiences, lessons, and guidelines of improv is to let go of judgment.
Don't judge yourself or others.
Don't think, "Oh this scene isn't going well," or "I'm not doing well," or "My partner isn't doing well." Because none of that is going to change the fact that you're on stage with this person. If you begin to let the shamed instincts you've learned take over, you will begin to judge and if you begin to judge, you will close down the scene.
Alternatively, if you embrace "what is" - then you are immediately building a scene.
Let's say a scene starts with Actor Charlie saying as he collapses: "Boy, I'm so tired from moving."
Charlie's partner then sighs because the last scene was about moving and so obviously this scene isn't going to be original and feels like Charlie always just copies whatever happened before. Doesn't matter what he says or doesn't say because it will come off as a block - which is to say it will come off as a dead note.
Now, Charlie's partner might think that Charlie always copies ideas, but that doesn't mean he can't embrace the moment anyway and join in: "Seems like EVERYONE's moving. But it feel so good." Or maybe, "Well, but thank goodness you're out of that dump you were in."
Charlie: "Hey, that was my Mom's house. I grew up there."
Again - this goes back to the idea of building and adding.
But you can't build and add if you're judging.
You might be judging yourself too. You might be thinking that what you say or think isn't funny or interesting. IT'S GOOD. It's good because it is. Whatever it is, it's good because that's what came to you. You can make anything work if you don't judge it. If you judge it, you'll shut yourself down. That won't work. That is the one thing you can't make work, your own judgment. You can even make other people's judgment on you work if you embrace it. But your own judgment, nothing to do with it.
So - what is the DO here? Embrace what is and you'll be able to make anything work.