1) Possess a green card and maintain residence in the U.S. for five years (three years if you are married to a U.S. citizen)
2) Application: Complete USCIS Form N-400 and pay the fee. As of 2017, the fee is $725. This includes the $640 citizenship application fee plus the $85 background check cost (also known as the biometric fee).
3) Fingerprinting: After your application is accepted, you will be given a date and address to a local office where you will be fingerprinted.
4) Interview and Naturalization Test: After your fingerprinting, USCIS will schedule an interview with you to meet with a USCIS officer who will go over your answers on your Form N-400. You will also be tested on your understanding of English and knowledge of civics (including U.S. history, geography, and government)
5) Attend the Oath Ceremony: Finally, you will go to a large public ceremony where you and others will swear an oath of loyalty to the United States. You will also be granted a certificate of naturalization as proof of citizenship.