dunno, rendering pitfalls for beginner? you don't need to render everything. As long you know the light source. Also gloss isn't always white, they reflect the background colors doesn't mean flat render is bad, there's great artists that used that style and made unique arts
if you're wondering (or not) of what happened to my cursed april fools unofficial adaptation of hot space cowboys/legend of the blue wolves you can "read" the chapter 1 (no prologue) test manga here (no dialogue/sfx, I gave up) : https://t.co/8gTtUwSQqW *warning : it's CRINGE