Depending on the airport you're flying into, there are often no longer declaration cards on the airplane. Your initial interaction may be with a computer kiosk; on that kiosk, I believe there is an option for landing immigrants. You'll get a receipt, the first round of customs officers will refer you to secondary screening and to the immigration clearance process.
If you do get a declaration card on the plane, read it - there may be an option for "I am landing as a Permanent Resident" or similar.