It may have been awhile since you've attended an elementary school, but it's a good idea to brush up on the school's rules. Field trip participants are generally required to follow school rules even when they are not on the campus. Obviously, certain activities, such as drinking alcohol or using tobacco, will be prohibited on field trips, but you may not think of lesser prohibitions, such as chewing gum or wearing open-toe sandals.
To be an effective chaperon, you will want to learn about the field trip and its intended outcome. If you will be visiting a monument, ask the teacher what he or she would like the students to learn about it. If it's a science center or factory, get some background on what the class has been studying. This way, you will not only be there to keep the kids safe and together, but you will be able to help them learn from the field trip.
Usually, chaperons for school field trips are assigned to small groups of students in order to organize the class and delegate responsibilities. Before you leave, introduce yourself to your group of students and learn their names. Tell them that if there are any problems on the field trip, they should report them to you. Ask them to stay together as a group or let you know if they need to go to the bathroom or somewhere else. Ask the children if they have any allergies, as this issue could come up if you will be eating on the field trip. Wear a name tag and give students a tip to remember you, such as, "Remember that I'm the one wearing the red shirt."
Field trips, especially those involving small children, can be very chaotic at times. Crowded bus rides, excited children and new scenery can be intimidating, but if you keep the right mind-set, you will have a much easier time rolling with the punches. Keep in mind that the purpose of the field trip is to educate students and to stimulate their social skills, so allow children to explore and question as they like, as long as they are safe and follow the school's rules.