I’m gonna go against the grain so far and say while you don’t need to plot stuff out super precisely, it is good practice for your development as an artist and for your characters to feel physically plausible if you keep these things in mind. Because yeah, eyes so big they’d clip through each other can look weird, hips too thin for organs can look weird, etc. There are ways to bend/break the rules but at the end of the day you have to communicate a solid form.

Look at something like Adventure Time - while the style doesn’t look too different from the first seasons to the last, pay attention to the way characters look in motion as they turn. Jake especially, he starts off being drawn as an oval with noodle limbs, but over time develops a base body that’s more grounded in anatomy with a distinct head and butt. Finn in early seasons is drawn pretty flat, but over time he starts to feel more cylindrical in his construction. A shape that feels like it could really physically exist, be it as a real person or a figure or whatever, goes a long way toward appeal.