In screenwriting as in life, communicating means being understood. And your goal with the script is to communicate – so make yourself understood. Be clear in your thoughts and what the audiences sees, and it will be clear on the page. This is your job as a writer and screenwriter.
TSL's Feature Format Template is an great tool to help you see how the script page should look as well as how to effectively communicate slug lines, title cards, scene descriptions, and dialogue, etc.