>>1666961Focus on medium distances (200 to 500 miles or so), that are long enough to be annoying by car but short enough that flights won't gain a real edge on travel time.
Still, make trains run longer distances than that, to also allow for people who just don't like flying to travel with them and to gain more flexibility. The key is having the right intermediate stops, so people don't just ride from one end-stop to the other.
Few, relatively short stops, only in reasonably large towns. Random stops are frustrating.
Comprehensive regional public transport so people can get to the train simple quick and cheap.
Make train comfy enough to not make the journey overly exhausting, don't go too fancy. Maybe offer food and drink as an option. Keep price to quality ratio reasonable.
Keep prices low. If going by car is 400$ cheaper for a whole family they won't take the train.
Avoid making things more complicated than they have to. Not having check-ins etc. is a major advantage over air travel.
Keep trains well maintained and clean. All corona-panic aside, people don't want a decade of dried piss on the toilet-seat, walls, floors and ceiling.