Announcement is something said, written, or printed to make know what has happened or (more often)what will happen, in writing an announcemen, keep tha following points :
- The title / type of event
- Date / time, place
- Contact person

Example :

“Announcement”

This is a news school year. Many new student are around and they need to know our school rules. Pease be helpful to them and extend curtesy to their parents. Thank you