To file for U.S. citizenship, you must:
Have had a Permanent Resident (Green) Card for at least five years, or for at least three years if you’re filing as the spouse of a U.S. citizen
If you apply for naturalization less than six months before your Permanent Resident Card expires, or do not apply for naturalization until your card has already expired, you must renew your card.
You can apply for naturalization before you receive your new Green Card, but you’ll need to submit a photocopy of the receipt of your Form I-90, Application to Replace Permanent Resident Card, when you receive it.
Meet certain eligibility requirements including being
At least 18 years old at the time of filing
Able to read, write, and speak basic English
A person of good moral character
Go through the ten step naturalization process which includes
Determining your eligibility to become an American citizen
Preparing and submitting form N-400, the application for naturalization
Taking the U.S. Naturalization Test and having a personal interview