I think the "rules" of looking good on the bike are exactly the same (and exactly as well defined) as off the bike. Especially if we're talking about normal people. Why would their taste in aesthetics change suddenly when it comes to bicyclists? If you want to look good on the bike, get jacked/shredded/swole/lean/dad bod or whatever physique you think looks good off the bike. Wear minimal/Hawaiian/street/logo/prep or whatever you think looks good off the bike. I personally love wearing minimal stuff off the bike (tends to not go out of style as quickly) and therefore try to do the same on the bike.