I have the 8-speed version. Shimano's instructions say to avoid shifting under load. You can often "get away" with shifting under a light load, but you might also hear various pings of pain from the hub as a result. Best is to pause your pedaling ever so briefly whilst you are twisting the shifter knob.

It's perfectly fine to shift while stopped though. That's a nice thing to be able to do at intersections.

The one thing I can think of is to eyeball your hub alignment from time to time. Scroll down to the bottom image in the following blog post, and notice the two yellow marks that I've zoomed in on:

Shifting Priorities ? Jonathan Gennick Living in the 906

It's super easy to eyeball these marks and adjust their alignment. There's a range of tolerance, but too far out of line can lead to trouble in shifting. Once adjusted, they aren't likely to go out of line.

Otherwise, I just ride mine.