Choose the destination. Usually, this is done by the teacher. But he or she might give you a field-trip topic to explore. Museums and parks are good starts.
Do your location homework. Book a date, ask the facility what preparations should be made and what to expect, and scout the location to plan and troubleshoot.
Arrange transportation. Reserve a bus if one isn't provide by the school, or see if parents will drive. Find out how much of the trip's cost will be covered by the school.
Do the paperwork. A few weeks out, send an authorization form home with the kids. It should include preparation items, a field-trip schedule and identification requirements. Also, make a packet for any additional chaperons with an itinerary, groups and preparation items.
Set rules and explain them to the class prior to departure.
Assign groups that are manageable for chaperons. Separate behavioral issues so no one chaperon has to deal with all of them.