Creativity and tenacity are great allies in this project but keep track of time schedules. You may have to consider letting go of an idea so that your final design can be thoroughly tested and things get done on time. Continually monitor the mass of your bridge during construction. For example, if the body of your bridge consists of three identical trusses, build one and extrapolate by tripling its mass to help predict the final mass of your bridge. Seriously consider building your prototype bridge with a mass no greater than 20 grams.
Wet glue weighs more than dry glue and makes weaker joints.
Be sure to complete your bridge several days before it is due in order for the glue to thoroughly dry. The spacing between the intersections of toothpicks greatly affects the strength of your bridge. Good glue joints make for good strength. Your bridge's strength is also dependent on its vertical height. Contrast the flexibility of a metal or plastic ruler held flat with the rigidity of the same ruler held on its edge.