@switu-There is a small factual error in one of your statements.You ARE NOT eligible for a green card if you entered the US illegally,even if you are married to a citizen.You need to have entered the country legally,ie you should have been properly let into the country by an immigrations  official at your port of entry.After that it does not matter if you become out of status,if marrying a US citizen.If you entered the country illegally,then even if you are married to a US citizen,you will not be eligible for   green card immediately.You will have to go back to your country and apply for the proper paperwork.This,i think,can take upwards of ten years.But this mostly applies to mexicans and not us nepalis since we all come here legally.  

@hatterika-legally, utilities and apartment are enough,but practically you might want to add a few other things-like a joint bank account,photos of you on vacation etc.If that is not possible then the first two should be enough.And you do not need a lawyer,they will charge you a hefty fee,and you will still have to fill up the forms yourself!The paperwork is simple enough that you can do it yourself.I did mine and it was no problem at all.If you need help send me an email,and i can help you with what forms need to be filled and sent.And no, i will NOT charge you,unlike a lawyer!lol.

But seriously,you need to realize that the officer will ask you questions which will be very hard to answer if you do not live with the person.For example he asked me who got up first on the day of the interview,me or my wife.And he asked her the same thing!If your answers do not match,you will be in trouble.But i wasn't asked too much cause we had  photos of the wedding and reception and also my parents were here.

But there are websites you can look up where they post general questions about what kind of questions are asked during the interview.Good luck.