Keep it professional and appropriate and avoid slang words or the use of acronyms - that way all ages will understand what is being communicated.

Make it clear on the very first day what the expectations are and then model those expectations.

It is important that the instructor and the students are on the "same page" with regard to communication tools. No one should be searching for where the information is located. if 1 person can not find /or did not see a message then reevaluate your communication.