I had a few lessons with a turner named John Davis, also bought my first tools and my bandsaw from him, one of the main things he taught me was function rules for functional items. sort of his quote, but it was a long time ago... "A fruit bowl is not a fruit bowl if it is so thin and light that it falls over when you drop an apple in it, and a goblet is not a goblet if it is so thick you can't drink from it."
When making bowls for yourself always leave the chuck mount on, then you can remount to refinish or change the shape, it is frowned on by other turners but if done well nobody else notices.
Art is in the eye of the buyer, here you can let your imagination run a bit wild. Personally I have absolutely no taste, if I turn something and think what an ugly monstrosity, it will probably sell, if I love it, I probably get to keep it! Myself and many other turners will look at a natural edge heavily spalted and split piece and think, wow that was hard / brave / insane to turn often before we look at it as a piece of art, we have all had a go at the knuckle tappers and the ones that would have hit us in the face if not for CA glue and duct tape.
Don't use varnish well not in a wood turning shop anyway the dust will drive you mad!
Don't use water or oil based colours unless you want to.
Don't mix oak and iron except where rust and staining is the objective
Bottom line is:
Keep your cutting tools (including abrasive) sharp,
Pay lots of attention to how your wood is connected to the motor so it stays where it was put.
Be aware of dust and use sensible precautions to keep it outside of you.
Decide the primary purpose of the piece, and blend form and function to meet that primary objective.
Look shamelessly at what everyone else is doing, there are only beads, coves and straight cuts available to us we can only choose size and materials, and people have been spinning wood for a lot of years, so everything has been done before, making your version of someone else's design is fine, if you think theirs is perfect get as close to it as you can, if you think it is almost perfect, then improve on it, you are doing it right when someone else copies you.
Most important is stay safe, and enjoy the process.
