I think the best thing we did when we first got our tandem was to plan the first ride as a "let's figure this thing out" ride. We didn't get on the road, but found a large empty parking lot first. Our specific plan was to try and get comfortable starting, stopping, and standing together without the distractions of traffic and road conditions to deal with. On that first ride, we put 5 miles on the bike just practicing the basics. Doing that helped us get those issues behind us in the safety of a parking lot, and our first "road ride" the following weekend found us both extremely comfortable with what we were doing together.

I think the other thing we do that really keeps my stoker interested is making most of our weekend rides a "destination ride" where we have a specific goal in mind...for example, we might ride a 50 mile loop with plans to stop at a specific cafe for lunch, or ride out to a small town for breakfast.

One additional thought that comes to mind is that my wife was badly intimidated by big hills. While I considered her a strong rider on her single, her climbing technique wasn't the best, and she generally hated anything that was half way challenging. Needless to say, I avoided the big ones for the first several rides, then when we started tackling them, I would talk her through the climb before we started. I would tell her what to expect in terms of shifting and our efforts. For example, I would tell her that as we started up, I would run down three gears on the back then shift from the middle to the small chainring on the front. Over time, she learned how we worked together and with the gearing on the bike to conquer the big climbs we encounter. Now we're both of the mindset that there isn't a hill out there that we can't climb together on our tandem!

Good luck, and have fun!