Hanging figures on a horizon line!! I learned this in college from a guy who used to do pencils for the big two, and it makes roughing out perspective 100000000x easier
Step One: draw a figure and a horizon line. See where that horizon line runs into their body (in this case, it's the top of the head, but it can be anywhere).
Step Two: for every person who is roughly the same height, the horizon line will run into the exact same part of the body.
BEHOLD! DEPTH!!! and I haven't even drawn vanishing points or a complicated grid or anything!! You could probably like, guess at where a sidewalk should be at this point, and not be that far off.
It works with any part of the body:
And if you have characters of wildly different heights, you can still use the trick if you compare the two of them:
Sometimes I'll start out just drawing a couple characters without thinking about the perspective, and I can use this trick to start figuring out the perspective of the scene by finding which parts of each character's body lines up, and drawing the horizon line there! THE MOST USEFUL FREAKIN PERSPECTIVE TRICK I HAVE EVER LEARNED