Forgive me if I flub up the explanation... It's a lot easier to explain these things IRL.
Everything regarding perspective relies on where your vanishing point and horizon line are. I made a guess here based on the shelf the character in the back was sitting on and ruled out from there. Even if you use a screenshot or a photo reference you need to figure out where the "box" your scene is sitting in is pointing towards and decide upon the vanishing point. You then go from there.
I'm just using a one point perspective here. You could have easily had the flooring pointing at a different vanishing point if you wanted to.
I added a blue line to show you how to best figure out people in perspective, but I realized that this is whole different issue with the panel to be tackled and that would be an info overload.