I agree with Chuck, this is part of the dealers responsibility and should be part of the final walk through.
I talked to the technician that set up my hitch and had him explain what we was doing and why. I also asked him about where to set the jack for a tire change.
To answer your question directly, my trailer was leveled in the dealers garage, the truck was backed up to it and was also level. The ball height was set 1 inch above the level TTs socket height, then the TT was raised and lowered onto ball. The WD hitch bar chain links were selected that made the TV and TT sit level.
The technician said, since the TT was empty I would have to adjust the number of links so the TV and TT sat level when loaded for the road.
This was the procedure for my truck and my trailer and my brand of hitch, done by a professional who was not afraid to explain thing to the customer. Your WD hitch set up could be completely different.
Take care
Twenty six foot 2010 Dutchmen Lite pulled with a 2011 EcoBoost F-150 4x4.
Just right for Grandpa, Grandma and the dog.