What are some ways to shorten detailed content when writing for a social media post for marketing a professional service?

Try to decrease the information to the NECESSITIES. Shortening sentences down to straight forward bullet points is also very helpful because you would be looking to attract the most amount of attention in as little words as possible.

Uploading an image would also be a plus because even if the text is relatively long, the image can be attractive enough for the user to put in the time and read the information.