What do you mean "using pre-made stuff is cheating"?

If you mean for the modeling, then I don't think it's allowed with most things out there. Most meshes come with EULA, which don't allow distribution of models derived from the original mesh.

Well, if the whole study is too much, it can start with the desk corner perhaps?

And I'm all for learning. Always :). And speaking of which: Do you know of any resource out there, which would list some basic generic DOS and DONTS for modeling? Just a brief list of rules with short descriptions of things which need to be avoided to prevent broken meshes, or ugly corners or weird planes, or stuff like that, and how to avoid it.

I can follow tutorials for modeling, but since I don't know these basics, I tend to be completely lost on my own and often end up with something weird looking or impossible to UV map (although that's another can of worms altogether).