@um9s

Peindre

I love that you're practicing form! I personally think perspective and form is the most valuable thing you can learn. So the reason it might look a little unstable is because your lines aren't drawn like they exist in the same scene. What I mean is that everything should be drawn while keeping perspective in mind because knowing where your vanishing points are will allow you to know which direction your lines should be going and how steep their angles should be. Lines going in the same direction should eventually converge on a vanishing point somewhere on the horizon line. But I know a lot of people don't like to go through the effort of plotting a perspective grid just to draw a box so instead here's something else you can try: Make all your lines going in the same direction parallel with each other. This still technically means you're following the rules of perspective, but when doing perspective your vanishing points can either be very close or very far apart. When they're close together they call it a wide angle lens. When they're far apart they call it a long angle lens. When your vanishing points are really far apart your lines will eventually become parallel. So all you have to do is make sure your lines are parallel with each other. I have talked about perspective more thoroughly in other critiques that you can look at on my profile if you are interested in learning more about it! I highly recommend learning perspective.