Parking 

When parking, try to avoid parking on steep grades. If possible, have someone outside to guide you as you park. Once stopped, but before shifting into park, have someone place blocks on the downhill side of the trailer wheels. Apply the parking brake, shift into park, and then remove your foot from the brake pedal. Following this parking sequence is important to be sure your vehicle does not become locked in park because of extra load on the transmission. 

For manual transmissions, apply the parking brake and then turn the vehicle o in either first gear when parked uphill, or reverse gear, when parked downhill. 

Uncoupling 

When uncoupling the trailer, place blocks at the front and rear of the trailer tires to ensure that the trailer does not roll away when the coupling is released.