poke the screw through a piece of masking tape with the sticky side of the tape toward the head. Place the screwdriver in the slot, then fold the tape up onto the screwdriver. Once the screw is well started, pull the screwdriver loose and remove the tape.
You may refer to a truss as the rafter, but it's basically the skeleton of the roof, carrying the weight of the frame and supporting the walls of the building. Trusses are very important to preventing the walls from bending or flexing, more so.