Too much storage in "other"

When I try to sync my iphone with iTunes, it fills about 10 gigs of storage space in "other". I have about 10 gigs of other data in music and apps, so it will not let my sync and I have no idea how to get rid of it. This happened when I was forced to update my itunes last night to download iOS 7 for my phone. Under normal conditions, I should have about 3 gigs free.