The U.S. government closely reviews all petitions for marriage Green Cards. Immigration officers look to expose what are called "marriages of convenience".
Marriages of convenience are cases of immigration fraud where someone marries another person so that they can get immigration benefits - such as a Green Card.
The immigration officer will ask you both a series of questions that may be very personal. The point of these questions is to reveal a functional and personal relationship between you and your spouse. You may be asked questions about your relationship, how you met, your finances, and the details of your daily lives and work. See a list of sample questions here.
The more you know about each other, the better the chance that your application will be approved.
If the initial interview is successful, you will then be granted a conditional Green Card. A conditional Green Card is valid for two years, after which you and your spouse will need to apply together to have the conditions on the Green Card removed.
To remove the conditions on the Green Card and get a regular, ten-year Green Card, you will need to file Form I-751, Petition to Remove the Conditions of Residence. At this time, you may be interviewed and your marriage examined again.