Interview Requirements
The interview will cover English and civics/history knowledge. Some people are able to skip the English portion of the test: see here to check if you are eligible.
Your English test will consist of speaking, reading, and writing. While there is no specific criteria listed for speaking, for the other two sections, you will read aloud one of three sentences or write down one of three sentences, respectively.
For the civics section, you will be asked up to 10 questions from the list of 100; you must answer at least 6 correctly to pass.
To study for the exam, see resources here.
Do not attempt to reschedule the interview unless you absolutely have to, or are sick. Doing so can delay the process. If you feel unready, you will have two attempts to take the test per submitted application, so you will have a second chance if necessary. If you cannot make the interview, let USCIS know as soon as possible at a field office.
After the interview, all that is left is the oath ceremony. Congratulations! You are almost a U.S. citizen.