Thanks
Well, I posted my experience of my AOS interview last month. You can do under search in here about my Baltimore AOS interview.
My advise is to be prepared with all the documents they need. The first thing you have to remember is the last three years tax returns. Your birth certificate, your passport and enough evidence of proof of marriage such as pictures, cards and letters. Joint accounts or savings, lease or anything that have both of your names in it.
Bring two ADIT pictures just in case. Prepare another I-864 just in case, but do not give it to the interviewer unless they ask for it. Some ppl said don't bother, but let me tell you something, better prepare rather than sorry. The interviewer will ask you things that you sometimes will wonder, but soon as they noticed that you can give them what they wanted, they will stop asking.
Sometimes they might ask you guys for separate interview, but it depends on your case. Not too worry coz' as long as you guys live together and have good marriage, it will be okay. When they separate you, they might ask personal questions like how many bedrooms in the house, which side you sleep, what you guys ate for the dinner or breakfast one day before or what brand of toothpaste you use. But as I said, it depends and not all ppl will get separate interview.
Start gather your evidence, bring all the originals and make a copy of each so when they want it, you can hand it over to them.
Sometimes even you prepared, your approval also depends on your background name check. If its done at that time, they will stamp your passport, if not you have to wait.
Good luck and be cool
There is nothing to worry if you prepared.