Most Helpful Guy
Wear a lot of short dresses, or shirts that show off your midriff. That should help. Go for black, red or dark colors. Heels probably would help, and learn how to perfect biting your lip when your interested in a guy.
Most Helpful Girl
I think generic advice is hard. It depends on your build, your face shape, and your style. Every woman achieves sexy in her own way, and complicating it is the fact that every guy has a different idea of sexy.