It is important to remember and know your rights.  The ACLU has a downloadable PDF with the below information:

Rights

• You have the right to remain silent.  If you want to exercise that right, verbally say so.
• You have the right to refuse to consent to a search of yourself, car, or home.
• If you are not under arrest, you have the right to leave.
• You have the right to a lawyer; ask for one immediately if arrested.
• Regardless of your immigration/citizen status, you have constitutional rights.

Responsibilities

• Remain calm & polite.
• Do not obstruct the police.
• Do not lie or provide false documents.
• Remember the details of the encounter.
• File a written complaint if you feel your rights have been violated.