Nina Agdal's rockin' bikini booty is in plain sight on the cover of this year's Sports Illustrated Swimsuit Edition. So how can you score a tight, perky rear that looks just as good in a thong? We spoke to some of Agdal's comrades at the Wildfox Model Beach Volleyball Tournament to learn how they make sure their tush is always camera-ready-and it's not all about lunges and squats! Try their tips now and you'll be ready to strut your stuff on the beach by summer.