What constitutes beauty is often a complicated matter, but here we simply sum it up as 'beefness'. Beefness, or physical ability is broken into stats: Strength, Health, TUs (speed) and Energy (Stamina). To increase beefness (and thus beauty), you need to train; the lower a stat, the faster it's likely to increase. Working out surely gets you there, but it requires effort. And there is a more fun way: combat. Hitting enemies with ranged and melee weapons or casting magic will not only influence related skills, but also gradually increase your beefness (and thus beauty).