Before camp begins, the camp staff should come together and choose a theme. The camp director may provide some instructions or guidelines, as a sports camp would likely have different theme options than a general camp or a language arts camp. Websites like Summer Camp Program Director have lists of possible camp themes, including Adventure Land, Fiesta, Treasure Hunters or Wild West.
Once the camp theme has been chosen, work together as a camp staff to determine how the theme will fit within the larger camp goals. Is there time or room in the budget for decorations or costume pieces relating to the theme? How can regular camp activities, whatever those may be for your specific camp, be modified to fit within the larger theme? A great way to make a theme memorable is to find a large final activity in which the entire camp can participate: a scavenger hunt, a final party, the construction of a theme-related object, or a showcase performance of campers' skills.
Now that your camp has planned its theme and worked with the staff to make it as fun as possible, it's time to get to work. Before camp begins, there should be a clear plan on how the theme will fit across the camp session(s). Make sure there are enough supplies to decorate the camp to fit the theme, and enough reading material or background material that all of the camp staff is ready to engage the campers in theme-related activities.
Once camp begins, use campers to help push the theme further. If possible, especially at sleep-away camp, provide campers with theme-related costume pieces. For day camps, encourage campers to come dressed in costumes fitting the theme. Award prizes - free time, a pizza party, or something similar - to campers or camp groups which do the most to engage and explore the camp theme.