Bring your original documents.
You need to have the original of any document you have already submitted with your application, or that you plan on handing to the officer during the interview. It is usually a good idea to bring the original and two copies. That way, the officer can examine the original, keep a copy, and you also have a copy of everything you gave him or her. On your copy, you can write the date and name of the officer that the evidence was provided to. If the officer cannot look at the original, however, he or she is allowed to not consider that document when making their decision.
Remember your dates!
During the interview, the officer will review your application with you and ask you the dates of many events (your date of birth, the date you entered the US, your marriage date, the date of any arrests, etc...) Memorize these dates and be sure they are accurate. If you give the officer a wrong date and it does not correspond to records they already have, the officer might think you are lying and deny your case. If the dates you give do not correspond to documents you have provided (e.g. the date you give for an arrest does not correspond with what is on the criminal disposition for that arrest), they may also think you are failing to provide certain documents and can deny you for that as well.
Submit all required evidence
USCIS can deny your application if you fail to provide the required evidence. This includes the basic evidence required for your application, as well as any additional evidence the officer may ask you to submit. Read the Form I-485 instructions carefully. Find the section that pertains to your applicant category and make sure you include all of the documents listed.
Be on time for all appointments
If you are late to an interview, USCIS may determine that you simply did not show, even if you end up arriving late. Different field offices have different policies on late arrivals. Some will try to accomodate you, while others will simply put you down as not having appeared. If you are considered to have failed to appear for your interview, even if you were only late, your application can be denied for failure to be interviewed and you will have to start the process from scratch. You should also be sure to factor in time to get through security lines at the entrance to the building, as most Federal buildings have strict security measures in place at all times.
Let the officer know of any issues you may have during the interview in advance.
If there is any reason why the interview may be harder on you than on other persons, for example because you are ill, have learning disabilities, memory troubles, or speech impediments, make sure you alert the officer at the beginning of the interview so that they take that into consideration when evaluating your answers.
Tell the truth.
If you take only one thing away from reading this article, let it be this one. Always, always tell the truth. If the officer suspects you are lying, or your answers do not correspond with information they already have in your file, you will be denied. Even if the officer does not catch a lie at this interview, but it becomes obvious later, such as when you are traveling or when you apply for citizenship, your green card can be revoked. Remember that officers have access to a lot of information, including previous applications that you filed or someone filed for you, travel information from federal databases, and access to local and national law enforcement records.