Glitter, belts, ribbons and spice, I call upon the 90's for bad character advice.
A character's visual appearance must not only embrace but give away 100% of their personality, because readers don't want to spend time figuring out who they are. A magical girl should only wear one colour in her whole outfit, preferably pink, avoid 'cool' colours because they are not as feminine, but it's ok if it's a tough tomboy character or a bookworm. You can further emphasize their personality by giving them Japanese names that directly mean their colour or elemental power! Try "Hikari", for a light themed or yellow magical girl, "Midori" for your tough green tomboy or "Sakura" for a pink/ love themed main character.
A main hero should have big spiky hair, it makes him visually distinct from the whole cast because we see many main protagonists that look this way. If you want your audience to fall in love with him, you can consider drawing him one of two ways. Maybe he is fighting for the love of his life, who is a maid, because a soft feminine maid makes the audience feel very sympathetic. Make sure to draw her a lot with her hands clasped around her chest, which will show that she's innocent and pure. He should look stoic and uninterested, but he actually isn't, you just can't tell past the constipated face because his life is really hard because the maid keeps getting captured and he's ready to retire and become a jaded alcoholic, the sequel. The other way I suggest is to make him really cool and happy and friendly, this is great if you don't want pretend he has a personality.
Villains need to show they are obviously villains, otherwise readers might be confused. Put some hard jagged edges and tatters in their clothes because villains are allergic to looking good. Unless he is rich, though. In that case make him look like a handsome prince but with a sinister smile, so you know he is up to no good. If you want to emphasize his character more, give him a tesla cybertruck and an instagram influencer entourage. You know he is lonely and miserable this way, because the models are being paid to be there.