This assignment is a pretty good way to just start a scene and jump right in। You are going to take a line of overheard dialogue and use it as a jumping off point for a writing exercise. First, do a Google search of the term "overheard." Go to any of the websites you find. Here are a couple you will come across:
Browse through them until you find a line you would like to use। Don’t spend a lot of time thinking about what you want to write after you choose a line of dialogue, just jump right into it. It’s also best to use this exercise as a sort of writing improvisation.
Once you find a line, just get to writing your scene। You can take a few seconds—no more than 20 or 30--to think of a possible setting or characters, but it’s really best to start writing immediately and discover those things as you write. An alternative to starting the scene with one of these overheard lines is to try and write your way into the line. I’d try to get to it sooner rather than later, probably by the end of your second page of script.
One of the great things about reading these "overheard" lines is that you do not know the context that they are spoken in, so you have to create it yourself। Starting a scene with one of these lines is also a great way to begin a scene quickly by throwing something at the audience and getting right into the conflict of the scene.
Also remember that writing is a lot of observing what is around you and then creating your own context for those events। Feel free to eavesdrop as you go through your day and you might overhear a line or short conversation that you can use in your scene work as well.
Now get to writing!