Male attractiveness is a lot more malleable than female attractiveness. Go to the gym, learn how to tell if clothes fit you and what colours suit you, always shower and shave, and get a decent haircut. You have now jumped 5-10% in attractiveness. Those are the biggest relatively easy gains. Posture isn't that hard to fix but it's hard to keep it fixed. After that there's the hard shit, becoming a more interesting, fun or rich person.