Drawing is fun and occasionally useful (e.g., sketching for math notes), while Inkscape is a nice and libre vector graphics editing program, and vector graphics are nice and scalable. So I decided to learn the basics.
Firstly, there is the "Inkscape: Guide to a Vector Drawing Program" book, which is linked from inkscape.org. And the "Learning Inkscape" section. But they are mostly about learning the program itself.
Then it is the time to practice, and I found that to be rather difficult: without any drawing background, it is pretty hard to draw something that you would not want to delete at once. But regular drawing tutorials, like on WikiHow's Category:Drawing, help with that. E.g., my first drawing in Inkscape:
And practice should make further ones better.
In addition to those tutorials, it does not harm to read on drawing in general. For instance, there are anatomy books for artists, and plenty of other drawing books (Goodreads is blocked in Russia by 2024 though).
And here is my third drawing, RMS:
"You Can Draw in 30 Days: The Fun, Easy Way to Learn to Draw in One Month or Less" appears to be a nice introductory book, suitable for learning with Inkscape instead of a pencil. Though it also feels oversimplified (e.g., drawing in perspective before even introducing it, and simplifying/not explaining it), and some would suggest to learn with paper and pencils first. A picture after its third lesson:
For drawing in perspective, wikihow and wikipedia may be helpful. There is a nice "Perspective Drawing Handbook (Dover Art Instruction)" book with examples, illustrations, explanations.
And here is a drawing in (quite possibly messed up) perspective:
