Quickie
Enter the scene as if you'll be there forever.
Photo by Marc Sendra Martorell on Unsplash
Never enter the stage with the idea to leave it immediately again. This is about actors entering a scene to deliver a single line, mostly aiming to throw in a quick joke as a waiter, messenger, or what have you.
Don't do that, since it's really just you by yourself having a little plan in your head. Moreover, always be prepared to be kept on stage by your partners, you don't know what's going to happen.