Great question Bill.
First, with some spoons, like the War Eagle, a swivel is built in. In others, not. Where no swivel is built in, I use a snap or I add an O ring. The loose fall flutters better than a spoon tied to the line. As for line twist, I simply allow the line to unwind from time to time. If I have spoon jigged all day, at the end of the day I cut the bait off the line and slow troll about 100 yards of loose line for five or ten minutes to remove all the twist before I stow the rod.
Good luck.