LIke the OP, I had done no towing up until fairly late in life (my early 50s). We now tow the trailer thousands of miles a year.
In addition to all of the good advice above, I would add the need for "heightened situation awareness," for lack of a better term. Check those mirrors like clockwork -- a fast clock. Look way, way ahead to see if traffic is slowing down, a light is getting ready to change, a fool is pulling out of a parking lot unsafely, etc. Because a trailer is so much less maneuverable than a single vehicle, you have to be hyper-alert.
The real challenge is at the end of the day -- you are tired, rush hour traffic may be building up, the angle of the sun is inconvenient, etc. That's why many of us choose not to tow more than 300 or 400 miles a day, if we can help it. When that hyper-alertness starts to become effortful, it is time to stop. I have done 500 miles into a setting sun, but not often, and not by choice.