One of the most important things is handling the trailer. When you deliver cargo (whether it is a quick order or consignment market) it is worth parking the trailer in the right place to gain all the EXP points (if you do not want to park it, just press [Enter] - your order will be finished, but your EXP score will be a bit smaller).
If you want to back-in your trailer, you have to learn how the trailer reacts to steering wheel. Find the perfect position, put in reverse gear and start driving. To turn the trailer let, turn the steering wheel right (and vice versa). Do not turn the steering wheel violently as the trailer may turn too much and you will have to start all over again.
When the trailer is turned enough, start turning the wheel the other way to set the truck straight. Continue going back, but do it gently, to keep the truck straight.
Park the trailer where you should. You do not have to be very precise, just wait until the white marks turn green. When that happens, close the order ([T] by default).
A quarry is a place where it is easy to park. Usually there is a lot of space and you do not have to go back.