Most Helpful Guy
You're already beautiful but if you want more sex appeal, you shouldn't have the cute smile as like I said it looks cute and young and not the grumpy sexy look straight guys go for.
Most Helpful Girl
Be more confidant.
You're beautiful the way you are, being confidant will amplify that.
If you just want to spice things up in your look though, try going to thrift stores and clearance racks, they have cool and interesting clothes. Dye your hair if you want. Change up your makeup routine.
Just making a change in general (and staying confidant about it) will be a beautiful change.