It really depends on the flight path and one's interest. As such, the best practice is probably to understand the flight path perhaps followed by normal landing and take off directions.

For me personally as one who spends more at high altitude while not in a plane flying by mountain ranges is high on my list - especially by mountains I have been on. Nothing like scoping out a climbing route from air. Best unexpected view was on flight to Japan that went further north than normal. We flew past Denali and the south face which a few years before I had climbed. Another unexpected view was a flight from Guam to Japan and flying by Iwo Jima. Seeing many other islands and then Iwo Jima one understood why it was so important to the US during WWII.