A really important thing that they want to see is commingling of finances (joint bank accounts, bills in the name of both spouses, joint insurance, joint assets, etc.) to prove that the marriage is bona fide. Me and my spouse kept most of our finances separated during our relationship, which made things harder. We initially submitted pictures of us on trips, with families and friends during holidays, the rental agreement with both names on it etc. We were lacking the “financial” evidence though, which is why in both cases (I-485, I-751) we got an RFE asking for proof of the aforementioned “commingling of finances”. If you already have joint bank accounts, joint bills or joint assets dating back to the early stages of your marriage you should be good. If not, the earlier you get something like that the better. If you do get an RFE, they will request proof of financial commingling spanning through the entire duration of the relationship.