Report the location/approximate location of the event. Be sure to distinguish clearly between where you are and where the event is thought to be happening (i.e., “I’m 5 miles north of Concord. The tornado looks to be about 1 mile to my northwest”). Be sure that reports that are relayed through multiple sources carry the time of the event, NOT the report time.
Any other details that are important – How long did it last? Direction of travel? Was there damage? etc.