Once you receive the letter informing you of the interview appointment, make sure to read it carefully. It lists not just date, time, and location, but also the necessary documents (many already needed for previous steps). Pay also attention to the second letter/checklist which also lists documents to bring.
Make sure you are proactive and collect all requested documents for the interview. However, if you are lucky, you may not need them. I ended up only needing passports, driver's license and green card, but I still brought the whole list of documents. Better safe than sorry!
On the interview day you will have to pass a metal control and take off your shoes, just like the airport controls. Thus, do not use complicated shoes nor too many accessories.
Once inside, walk to the window to get a number and wait until they call you. Then, they will bring you into an office to interview you.
Part of the interview is spent providing the documents the interviewer asks for, and the other part is the exam. The interviewer will ask you between 6 and 10 questions (if you pass all of them it will be enough with 6, if you fail any, you will get more. You can fail up to 4), and then you will be asked to read a sentence and write another. You will also get to answer all the questions on the last part of the paperwork, the ones that ask you if you are a terrorist, a communist, a duke,....
Once you finish, they will give you the document N-652 with the result of the interview. Then you will go back to the waiting room to wait until they give you document N-445, the appointment to the Oath Ceremony. In my case, the appointment for the Oath Ceremony was for the week following the interview.
If your interview is in Charlotte, NC, I can tell you that Oath Ceremonies are done on Tuesdays and Thursday, and if your interview is such a day, you may be offered to do the Oath Ceremony that same day.
Once you receive the letter with your interview appointment, if it does not work for you we can now see what to do about it to change it.
First, read the letter carefully, and if your letter is like mine, there will be a brief sentence in the first paragraph indicating to write a letter to the office explaining why the change of date. The address of the office will be written at the end of the letter.
If there is no such indication you can call the number you find on the letter, it should be (800) 375-5283. However, it is not the direct phone number to the office, and they ask for a whole month to make sure the office receives the message. Thus, I would still write a letter to the office.
In the letter, mention your Alien number, the receipt number associated to the case, and the date in which the case was received (all these numbers should be in the header of the letter, in a rectangle). Besides you can add the explanation of why you cannot assist and have to change the date.
One more recommendation would be to send the letter with a tracking system to ensure the letter arrives to destiny.
Once they receive it you can check the status of your case as explained here or calling (800) 375-5283, for which you will need the receipt number.
Finally you will receive another letter with a new appointment.
That simple.
Shortly after 2 months from the Biometrics I receive a letter with the appointment to the interview. The appointment is in about a month; therefore, if you want to wait to receive the letter to start studying you would have time. However, I would recommend you at least read/listen the questions and answers once or twice in advance, that way it will be easier when starting to study.
Anyhow, I am afraid the given date is not a convenient one since I will be on vacation. The question is, how do we change the appointment?
You can read about it here!
Wherever you find yourself in the naturalization process, and once you have received the receipt letter (form I-797) or an email note (as long as you filled the form G-1145), you should have all you need to check your status.
On the receipt or on the email you will find a receipt number. With that number yo can go to the Official Website of the Department of Homeland Security and click on "Check your case status", or click here and insert the receipt number.
You may see something of the following sort, always depending on the status of your case.
Good luck, and I hope it is good news!
Three weeks after sending the documents I receive a letter with the appointment for the biometrics. The appointment is within 2 weeks!
For the biometrics appointment you have to bring this letter with the appointment and the green card as ID.
~~~~~
I showed up half an hour earlier and I spent there about 30-40 minutes. It was quite fast.
Firstly, and after showing letter and green card, you receive a paper to fill, and a booklet like this with the questions and answers to study for the interview. The paper you will have to return to the staff filled after standing in line for about 5 minutes, and the booklet is yours to keep. Once you have given the paper, you will have to wait to be called. It may take between 5 to 10 minutes before they call you to take your finger prints and a picture. After that, you are asked to fill a 2 question questionnaire and ready!
Now you just need to wait again to receive another letter with the information of the appointment for the interview/test. Keep on studying!
Well,time to study!
Here you can read and download (one by one) the audio of the 100 questions with answers for the Civic test in mp3 format. In the test they will ask 10 of the 100 questions, and as long as you get 6 right you are done. It does not seem hard.
Here you can find study material for the English test as well as for the Civic test.
Keep in mind that "You have two opportunities to take the English and civics tests per
application. If you fail any portion of the test during your first
interview, you will be retested on the portion of the test that you
failed between 60 and 90 days from the date of your initial interview."
PS: As you go for your Biometrics apt, you will receive a booklet and a CD with all the questions and answers, you may or may not want to wait until then to study
Are you ready to send all the documents? If you want to add a cover letter you can check this post. Also, if you want USCIS to inform you of when your application has been accepted, you can fill the G-1145 form which can be also found here. Once your application is accepted, they will inform you within 24 hours via email.
Well, now we got it all, so where do we send it?
I recommend to read the more detailed information here (then click "Where to File"), from were I pulled the following information. Roughly, here is the list of where to send the paperwork:
"If you live in Alaska, Arizona, California, Colorado, Micronesia, Guam, Hawaii, Idaho, Kansas, Mariana Islands, Montana, North Dakota, Nebraska, Nevada, Oregon, Utah, Washington, Wyoming, send your application for U.S. Postal Service to:
USCIS
P.O. Box 21251
Phoenix, AZ 85036
If you live in Alabama, Arkansas, Connecticut, District. Of Columbia, Delaware, Florida, Georgia, Kentucky, Luisiana, Maine, Massachusetts, Maryland, Mississippi, North Carolina, New Hampshire, New Jersey, New Mexico, New York,
Oklahoma, Puerto Rico, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Virginia, Virgin Islands, Vermont, West Virginia, send your application for U.S. Postal Service to:
USCIS
P.O. Box 660060
Dallas, TX 75266"
Now it is time to put everything in an envelope, write the address, send it and wait to be informed that the application has been accepted (as long as you sent the G-1145 form), and wait for the biometrics appointment.
Personally, I sent it through U.S. Postal Service with tracking to know that it reaches its destination safely. The cost was $5 and some change, and with the code you can follow the letter's path here. Sending it on a Saturday I know it arrived to destiny on Monday, and on Tuesday it was picked up. I received notice via text message that my case was received 10 days after sending it.
While you wait you can start or continue to study for the English or Civic tests. For more information about the tests and where to find study material read this post.
Once you finish, they will give you the document N-652 with the result of the interview. Then you will go back to the waiting room to wait until they give you document N-445, the appointment to the Oath Ceremony. In my case, the appointment for the Oath Ceremony was for the week following the interview. 
