Consult with an immigration attorney to determine whether you've met the residency requirements.

Be prepared to provide documentation of your travel history and residency.

Consider applying for a re-entry permit if you need to travel abroad for extended periods.

As a Green Card holder, to apply for U.S. citizenship, you must meet the residency requirement of 5 years of continuous residence, with no trips abroad longer than 6 months, or 3 years if married to a U.S. citizen.