Saw this on This Is Colossal and wanted to try it out. So far have just done a couple quick doodles, but it's really fun!
Here you can see I have done two doodles in slightly different planes, so when one looks 'right' the other is slightly skewed. The bricks in the wall are drawn normally, because the plane of the paper is the right plane for the wall, so the skewing occurs on its own!
If you use the side of the vertical side of the paper as a wall, you can just draw normally on it, and it will skew itself properly. If anything protrudes from the wall, however, it has to be skewed in the drawing to look correct. The fire hydrant top is very skewed if you look at it from straight on because it is drawn to look as if it is in front of the vertical plane of paper. On the right is looking at the paper from the other side, to show how odd the paper looks if you don't have just the right angle. It is quite frustrating to draw these without any sort of form to keep the paper bent properly, I need to find a good cardboard box or something to make a bent easel.
For another way to draw 3D in 2D, click here