A good source of information is the International Program for Students.
If you have full financial support from your government, then we only require an iBT TOEFL score of 88. If you need financial assistance, then essentially the only source is the graduate teaching assistantship. For this you must present an iBT TOEFL score of at least 100, with at least 22 in Reading, 22 in Listening, 21 in Speaking, and 24 in Writing. Upon arrival at USC, you will also have to take a test of written and spoken English in order to be approved to teach.