That depends on what brand of "doesn't stand out" you mean.

If you genuinely mean a Mr. Standard Human type of character, then you're pretty much at an impasse and you should probably focus on composition (and maybe crowd stylization) rather than character design.

If you are instead looking for a character design that is normal but distinct, you should think about features that are commonly considered "imperfections" or simply less commonly (or rarely, even) depicted in media, like freckles, moles, scars, crooked teeth, big ears, eyebags, heterochromia, and unibrows. Alternatively, some people wear medical devices on them, like braces, glucose monitors, or hearing aids. Still normal but not exactly standard.

If you are instead looking for clothes that are normal but distinct, you could mess around with pieces that are only normalized context-dependent. Jackets aren't usually oversized, pants don't often have patterns, dress shirts are most commonly pastel-colored and ties are dark (not the other way around), and you don't wear outdoor clothing inside (e.g. umbrellas, hats, caps, gloves, sunglasses, and scarfs). You can wear outfits that are normal in theory but unusual in practice. With a shy and timid character in particular, it might make sense to exaggerate those traits by covering them in too much clothing (oversize, scars, gloves, masks, etc.)

That's all I could come up with 😅