From my sketchbook practice with dominant straight lines. In fact, I force my pen to snap to vertical and horizontal as much as possible. I'm keeping the values simple to a max of 4 shades and, I aim for a time spent per sketch somewhere between 1-4h.

Youtube playlist with timelapse videos for my this exercises:
https://www.youtube.com/playlist?list=PLd6jN9QLncBAobUE2dzYUO2B6XMz50RQG

The sketch are done primarily in 3 steps:
Step 1. Layout and proportions
Step 2. Basic depth as max and min shades
Step 3. Adding the details