Start your biga the day before you plan to bake the bread.
Mix flour, water, and yeast. The water should be close to room temperature. Since the biga is relatively dry, mixing is a little tough. Wetting your fingers in water helps (don't flour your hands at this stage); make a cutting motion with your fingers through the ingredients. After cutting a few times, grab the dough and fold it over itself. Combining these two methods for a few minutes will mix the dough well.