Have enough designated “crew leaders” so that there is one leader per 3-8 estimated volunteers. Crew leaders should be well-trained in the task at hand and in tool safety, so that they can instruct and supervise the volunteer work. For projects such as vegetation clearing, digging, and planting, crew leaders can be trained in a short 1-hour session. For more-skilled projects such as concrete pouring or carpentry, crew leaders should have previous, significance experience with the type of construction and have spent time reviewing the project at hand.
In addition to the crew leaders, your team should include:
At least one leader who can greet volunteers as they arrive, ask them to sign in, and direct them to projects that need to be done.
At least one leader who can be a “runner,” going between projects, making sure they have the materials and tools needed, troubleshooting and answering questions.
(Optional) a volunteer to take photographs and document the work
Consider having a T-shirt or badge so that leaders are easily-recognizable.
In addition to the tools and materials required for the project, each volunteer day should have:
A sign-in table
A first aid kit
An emergency plan that all crew leaders are familiar with, in case of accidents
Drinking water
Snacks and drinks (optional but always a great idea!)
Water access for rinsing off tools and hands
Access to restrooms
Start off the day with a welcome session for all volunteers that includes basic safety precautions and proper construction/planting methods.
Other words of advice:
Make it fun! Turn mundane maintenance tasks like weeding into games (competitions) or art projects (build something out of the debris). For example, the annual replastering of the mud mosque in Djenne, Mali becomes an annual celebration and cultural event: https://www.pbs.org/video/great-mosque-replastered-ickx10/
Consider planning some kid-friendly activities (with crew leaders) that are occurring alongside projects that might not be suitable for young children.