I have been triking about 15 years. 11 years on a VW based Trike Shop Runabout, the past 4 or so on a 1995 GW1500 Motor Trike. Feel free to pick my brain (such as it is)! Pics of both are posted in the garage.
For new trikers, especially those coming from a 2 wheeler, a few tips:
1-Keep that front wheel in the middle of your lane.
2-Point the front wheel in the direction you want to turn (no countersteering!)
3-Don't put your feet down at a stop.
4-If you think you will be able to reach out and touch something to the side, you're too close! Watch out for curbs, toll booth & gas pump barrier poles, etc.
5-When you hit a pothole or bump with one of your rear wheels, the bars will shake a bit. Don't worry, this is normal. The effect is a little more pronounced with solid axle rear ends.
6-Add extra time at stops on a ride for answering questions from interested folks asking questions about your ride, from both two wheel riders and nonriders. (We could retire if we got $1 from every little kid we gave a quick 5 minute ride around a parking lot, and a couple of parents, too.)
7-Don't worry about the small decrease in gas mileage. You now carry more weight, bigger wheels (and an extra one) and there are 2 air brakes right behind you, also known as "fenders"
8-The soreness around your mouth and cheeks is from the extra big smile you will have for hours at a time. It doesn't go away, but don't worry - you'll get used to it.