Well J&T,
Practice, practice, practice--like most things getting that spatial perception for where the ball is in relation to the tow vehicle takes time...
I always try to line up straight with the trailer, if it's too tight, at least line the ball up with the hitch. Back up to where you figure it is, then go have a look at what the difference is.
Make any angle adjustments based on how much out of line you were.
Then I use my foot or a stick, leaf, etc. on the ground in relation to the door hinge to determine distance moved by the ball--you know, sitting in the truck with one foot on the brake and the other on the ground is not 100% safe for sure, but...
50% of the time I get it after one look, 40% it takes two, 5% three, the last 5% isn't fit for a family friendly website!
After a while you will be able to trtanslate those small distance and ancles from the drivers seat.
Good Luck!