Good topic. I struggle with this too. What Phil says is accurate and you'll see the skier, slope, and horizon in a lot of my shots. Also, for me it sometimes just comes down to luck and volume, take a lot of shots and a few will capture steep.
On Larkspur beside the Zuma lift on backside of Arapahoe Basin:
This is a fairly steep blue square run,
@Ken_R
but I made it look flat on the same day in May 2019 with
@Tony S
One of my favorites of my "home" hill, Blue Knob, PA, Vernette skiing in 2010 on Extrovert trail. This was lucky. I just snapped the shot quickly looking back over my shoulder.
Of course, shooting people in real steep terrain can help too
Corbets at Jackson Hole 2015, older anonymous skier:
Delirium Dive at Sunshine Banff, 2018
I post more later that maybe will offer further explanation.