IN THE AcTING BUISNESS!!!?

hi this spring i just found out at my school that our play is going to be high school musical. i really want the part of gabriella or sharpay but i dont have long or blonde hair. i also am pretty good at singing but know i need to improve a little because my school has a lot of competition in the drama department. but i want this more than ever!!!! what do you suggest i do to get better at singing and to improve my chances of getting a lead role? thankssss