Imo that's the best way to learn, thrown to the wolves. Sink or swim, if you're not cut out for it you'll find out real fast. Pretty much what happened to me with food service. I think my trainer had like 9 months experience
Basically, think it through, and make it as easy for yourself as possible. Move your tandems if need be. Anyone getting fussy because you're being safe and careful should have left sooner... Not your monkey not your circus, not your problem...
While not in a semi, but in a bus, I had a chance to take this picture today. I was forced into an alley dock today and the front tire tracks are useful in trying to make a point. Note how much the front tire offtracks. In a semi your drive tires would need to do the same. One of the most common issues I see is that people don't: A) realize how far a semi must move before the trailer responds (about 10 feet) B) waste a lot of space by rolling while turning the wheel. As others have mentioned learning to back is not a spectator sport. It requires practice.
I just learned by doing over and over again. I can back up fairly easily at oatka now which is a very tight plant. It gets much more difficult mid summer with the sun beating down, you end up in a situation where it's much brighter outside then inside the building. My advice, clean your mirrors when in situations like that. Take your time. When in doubt get out and look. Pull forward and readjust when necessary Tankers tend to be a little easier then Van trailers simply for the fact you can see more around the trailer curves.
You should be backing every time, when I was a trainer, when we got fuel and did our 30 min break, guess who backing in to open spots at the truck stop, yup the trainee. ‘At the shipper and consignee, the trainee was backing up, I would throw them to the wolves but they would learn quick.
Good tip. I forgot to mention that. Dirty mirrors esp at night with lights shining at you/sun during day makes it almost impossible to see with dirty mirrors/Windows
So when you're looking at your target in the left mirror, you have a parking spot that has two edges, or boundaries, if you will. Your goal is to get your trailer inside these boundaries. What I do (after G.O.A.L.), is picture an imaginary straight line stretching from the NEAREST BOUNDARY. Basically it is an imaginary EXTENSION of the boundary stretching into infinity. You can disregard the other farther boundary. More on that later. So what you want to do is have your pivot tandem wheels hit that imaginary line at a 45 degree angle (in a perfect world). Anywhere between 45 and 60 degrees will do. If you hit it at less than 45, you will most likely undershoot and hit the near trailer. If you go over 60 you will have a hard time getting under it enough for it to fit into the hole without hitting the far trailer. Once you hit that line at the correct angle with your rears, you can start to get under it and follow it in. The reason you don't have to pay attention to the far boundary is that if you can stay within a foot of the near boundary, you will have 2 or 3 feet of clearance on the other side. Most spots are 11-12 feet wide. Make sure your tandems aren't up front! With your lack of experience, you WILL be fooled and the trailer swing will obliterate that far trailer. The farther up the tandems are, the farther you have to be from the truck line to start the maneuver. If you can't picture this in your head, just reply back and I will draw you a diagram and post a pic here for you. Also, someone else mentioned the snake maneuver. That eliminates the need to hit the imaginary line at 45 degrees because the maneuver itself already took care of that for you.