Fill out form I-751 ASAP and get a money order for $680 ($595 for the form and $85 for biometrics).
Send some copies of evidence along with the form (mortgage or lease documents, joint bank statements, birth certificate of any children born in the marriage, joint bills, joint insurance, photos, affidavits, etc).
Since your greencard expired only 2 days ago, I would go ahead and send it out today itself so it can get there by end of the week.