There are many documents and evidence that you can submit in support of your I-751. The documentation should be tailored to reflect the true nature of your relationship with a focus on the commingling of your finances. Remember to timely file it; within 90 days immediately preceding the expiration date.
You may apply for removal of the conditions on your lawful permanent residence 90 days prior to expiration of your green card. You should include documentation to illustrate that you and your spouse remain married and reside together as a married couple (joint lease agreements, bank accounts, other joint accounts, car insurance, birth certificates for children, etc.). If you and your spouse are no longer together, you must provide proof that the marriage was entered into in good faith and not for the purpose of evading immigration laws and you will need to request a waiver of the joint filing requirement. The timing of filing the I-751 will depend on whether a divorce has been filed, finalized or is currently pending.
Additional information about the time to file Form I-751, evidence to be included, filing fees, etc. can be found in the directions for Form I-751 found on the USCIS website. I have included a link for you below.
Six months prior to the expiration of your greencard you will have to submit several documents attesting to the bonafides of your marriage. I hope that it works out for you and wish you the best.
Legal disclaimer: The response given is not intended to create, nor does it create an ongoing duty to respond to questions. The response does not form an attorney-client relationship, nor is it intended to be anything other than the educated opinion of the author. It should not be relied upon as legal advice. The response given is based upon the limited facts provided by the person asking the question. To the extent additional or different facts exist, the response might possibly change. Attorney is licensed to practice law only in the State of Massachusetts. Responses are based solely on Massachusetts law unless stated otherwise.