Place heavy boxes on the bottom. Place boxes on top of each other if they are equal in strength. Smaller boxes on top. Long items on sides. Mattresses, box springs, sofas and table tops.
Mirrors go upright.
Odd shaped items go along the walls. Place odd items on top of the load. Roll up rugs and place them lengthwise in the center. Lock the truck when it's loaded. Check to be sure everything is sitting properly and tied down securely.