One lesson learned riding a tandem is that there are different ways to ride out of the saddle. Specifically, you don't HAVE to flop the bike back and forth, and if you've got another rider back there, flop it one way and it doesn't come back easily! So vary technique accordingly.

I find, riding my single bike, a lot of times I stand on hills rather than downshifting, and a part of that is because I'm riding with other people going slower, so I don't have to get top performance. Otherwise, sit and spin or whatever gets you up the hill fastest, then stand as needed for a butt break, not just for increased effort.