Great that you are looking to get a stronger handle on perspective! It's a fantastic tool that will only make your work stronger.
You can see from my draw-over that I'm hitting similar concepts as others. But here's specifically what you would want to keep in mind on low angle POV like this:
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While this might seem like a one point perspective. It is actually a two point. Only instead of the two points being on the left and right of the horizon line (HL) they are aligned vertically. The first vanishing point (VP) is on the HL where the blue and green lines converge. The second VP is waaaaaaaaaay off the top of the picture plane where the red lines converge.
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The next thing is that for the image to look right all the figures need to be on the ground plane. That's where the blue lines (orthogonals) come in handy. I used the door figure as the basis. Then drawing blue lines from the HL VP I created a ground plane "grid". As long as the feet of all your figures connect with one of those ground plane orthogonals the viewer will perceive all the figures as realistically standing on the floor. (in the current drawing the foreground lady is either on a different ground plane or she has super stumpy lower legs)
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Speaking of the figures -- they will need to be adjusted slightly so that they converge on the vertical VP (the red orthogonals converging way off the top of the image)
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I did make the door feel more realistic by changing the angle at which the door is open, because doors rarely open exactly at 90 deg to the wall. But you can see that doing this introduces two new Left and Right VPs. But those are easy to track to the HL using the purple orthogonals.
-Finally its just a matter of making sure the light grid is a series of consistent square planes.