Strap from the triple clamp or the frame by the bars down and out. Compress the suspension within reason. Lock the brakes or chock the wheels. This can be done by screwing blocks of wood to the trailer deck. Also, block the tires from slipping sideways with either chocks or straps. Secure the rear of the bike in a suitable manner.
Don't forget, the most dangerous situation occurs when you stop abruptly or hit something head on. Make damn sure you strap the bike rearward.