Backing and Parking Combination Vehicles
Backing a combination vehicle is a mirror skill and a patience skill. Know the two basic maneuvers: straight-line backing (back slowly, use both mirrors, and make small corrections) and offset backing (back into a lane offset to one side, using the mirrors to judge the trailer's position). Alley dock and parallel dock backing are the common test maneuvers. The core rule: steer the trailer, not the tractor - to move the trailer's rear left, turn the wheel right while backing, and vice versa. Get out and look (GOAL) whenever you are unsure; a spotter or a walk-around is always acceptable.
Traps: questions about which way to turn the wheel (the answer is the opposite of what many expect because you are backing), questions about backing with a doubles setup (back only the rear trailer, and only in a straight line if possible), and questions about parking - set the parking brakes, use wheel chocks, and on a grade turn the front wheels toward the curb (or away from the curb with a curb present, depending on the rule; know your state's rule).
Rule of thumb: back slowly, no faster than a walk, and correct in small increments. If the trailer starts to jackknife, stop, pull forward to straighten, and try again rather than fighting it.
For parking, choose firm level ground, set the spring brakes, chock the wheels, and lower the landing gear if you are dropping the trailer. Never leave a combination unattended without the brakes set and wheels chocked.