Try to get branches with a similar diameter (between 1'' and 2'' ). Branches found on the ground might be too dry and weak. Once the branches collected, cut them with a saw. Make the parts 2'' long. Remove the small twigs sticking out. Depending of your design, you'll probably need hundreds branch sections.
Once you have all parts, drill a 1/4 inch hole trough all of them. Make sure the hole is centered.