Endorsement from your ISO.

1) You need the international advisor of your ISO to endorse your I20, and make sure it's current.
2) Make sure your name is on SEVIS. If you are a spouse, then make sure the student's/your spouse's name is on SEVIS.
3) You need a valid visa(the stamp in your passport) to reneter US. Make sure you have that. If your visa expired but the status is valid, then you need to get a visa either in China or in Canada/Mexico before you can return to US.