In this video, Vladimir London, a Life Drawing Academy tutor (https://lifedrawing.academy/), will show how to draw a square in a 45degree view. The vanishing point is located on the horizon level. To begin with, I will explain the plan. Here's the square that is used to draw a smaller square that is rotated at the 45degree angle. We can now draw it in perspective. The vanishing lines of the square in onepoint perspective, which is marked in yellow, converge into the vanishing point. The 45degree square is inscribed using 4 points of its corners. A circle is inscribed into that square. Note that the boldness of outline follows the aerial perspective rule. The frontal part is bolder and the rear part is slimmer.

In the next drawing, you can see that the horizon line is placed in the middle. Vanishing lines are converging into the vanishing point on that horizon. I will draw four squares in perspective two above and two below the eyelevel. Once again, we draw squares in onepoint perspective and then use them as guides to build squares rotated at 45 degrees. Check how outlines become bolder from back to front. To learn more about drawing in perspective, take the Life Drawing Academy course https://lifedrawing.academy/free