The phrase "listen carefully" is correct and usable in written English. You can use it when you want to emphasize that the listener should pay special attention to what you are saying. For example, "Listen carefully, I only want to explain this once.".
Listen carefully now.
Listen carefully everyone.
Now listen carefully.
People don't listen carefully.
But listen carefully.
We listen carefully.
As they talk, listen carefully.
Since I tried Ludwig back in 2017, I have been constantly using it in both editing and translation. Ever since, I suggest it to my translators at ProSciEditing.
Justyna Jupowicz-Kozak
CEO of Professional Science Editing for Scientists @ prosciediting.com