This is a good way to start a tandem. However, Charlie Heggem at Cirrus taught us a variation that we prefer.

-we straddle the tandem.
-I rest my left thigh on the top tube, and clip into my left pedal. My left thigh is almost horizontal. This position is more comfortable than squeezing the top tube with my inner thighs, and also provides a wider platform to keep the tandem upright.
-my stoker sits on the saddle and clips into both pedals. Our left pedals are now in the 10 o'clock position.
-when we're ready, I say "go" and we push down on the left pedal. Since she's fully clipped in, my stoker can easily power up. While pushing down the left pedal, I step up and back onto my saddle.
-we continue to pedal while I ease into my right pedal.

My wife was skeptical about clipping in both pedals. But after a few practice runs, we find that this method is smoother and more consistent.

To dismount, I unclip my right pedal and get ready to support the top tube with the left thigh. My wife remains clipped in.

Charlie also showed us an easy way to make tight turns. While pedaling slowly, lightly squeeze the front brake to make a tighter turn.