Try to remember what happened, who was present, the time it happened, where it happened, and why it happened. These notes will be extremely important to the officer when you are interviewed. Seldom does law enforcement get a complete description, but many times a partial description is enough for identification and apprehension. When an individual is present at the scene of a crime, he or she is often scared or excited and not paying attention to detail. Many times investigators, in interviewing witnesses and victims obtain very different description of the same individual from the witnesses or victim.
Association is one of the best ways for untrained persons to recall physical descriptions.
Weight is tricky. The best bet is to make a comparison with someone you know. Eyes differ in size, shape, color, and clarity. A suspect was once arrested because a witness remembered he had one brown eye and one blue eye. Complexion might be important, especially in describing Black suspects.