First and foremost, take it seriously.Even though it is just a drill and even though you have participated in these since you were a small child, this does not mean that you should not treat it as though you were in an actual emergency. Children will take their clue from you. If you talk about how silly it is or act as if it is not worthwhile or important then students won't respect it either.
Know your escape route beforehand.This is especially true for new teachers. You want to look in control and in charge because this will help you keep the students under control once they all get to their destination. Make sure that you talk with your fellow teachers BEFORE the actual fire drill day so that you feel confident of where you will be going with the students.
Review with your students your expectations before your first fire drill.Make sure that you let your students know where you will be leading them in case of an emergency. Explain to them what your expectations are in terms of leaving, walking through the school, staying together, and gathering in the assembly area. Explain the consequences of misbehavior. This should be done early in the year.
Remain calm.This seems like a given but sometimes the teacher causes more problems than the students by not remaining calm from the beginning. You should act serious and in charge. No yelling. No getting excited. Just tell your students to line up calmly.
Have your students line up and stay in line.When the fire alarm goes off, have the students immediately line up at the door. This will help them remain calm and you keep control. Single file works well, even with older children.
Grab your grade/attendance book.Make sure that you take your grade/attendance book with you. First, you will need to take roll when you get to the assembly area. Second, you will want to have the pertinent course records in case there truly was a fire. Third, you do not want to leave this unattended just in case some students planned mischief during the fire drill.
Check the room and lock the door before you turn out the light.Make sure to check that you haven't left any students behind in the classroom. Turn out the lights and lock the door. Locking the door is important so that no one except the authorities can get into your classroom while you are gone. Students will probably leave their purses in the room and you might have some valuables you don't want disturbed. This action ensures that persons who are up to no good will stay out of your room.
Lead your students quietly through the school to your destination.
Like it or not, you are judged on your students' behavior. Therefore, try to maintain control as you walk through the school. Students should not be stopping off at their locker, going to the restroom, or visiting their friends from other classes. Make this very clear to your students before and during the fire drill. Make sure to have consequences if students don't follow your rules.