Healthy plan for looking good in a bikini?

i am not at all fat. i wear a size 2 and am 5'4 116lbs. i am almost 15 years old. i am trying veganism after christmas. i have a whole cookbook full of vegan recipes. i am thin, but not in shape and somewhat flabby. i would appreciate it if you could give me tips on what to eat to build muscle, but it has to be vegan. i have an exercise ball, treadmill, and i do yoga. what exercises should help give me a firm body?