Also just adding a community note, drawing actual boxes in front of you is great practice and a very traditional art school exercise! It can really start to make perspective feel more intuitive and real, and I think the study is great training on other levels as well - light and shadow (if you just have one light source), and observational drawing in general. Here are a couple of examples - I just use some random shoe boxes and amazon boxes of different sizes and set them up with a single light source. I drew these on newsprint with charcoal, but of course you can use whatever - pencil and sketchbook is great. This reminds me that I'm overdue for another round, I think this is one of those exercises that's always a great warm-up / tune-up.

This very subject is covered in the first section of the entire free course. https://geometrydash2.com

Google 'Drawabox'. Its a full free course that tackles this very topic in the first section.

Perspective mistakes are relatively easy to spot. Just take a ruler, extend the lines you drew, and see which lines are off.