People living in the U.S. must abide by the federal, local and state laws of the country. America grants certain rights to the people who have been granted permanent resident status (green card status) in the U.S. Green card holders can remain in the U.S. forever. But to retain their legal status, they need to abide by the laws of the U.S. If not, they might lose their green card status. They need to actively protect and maintain the legal status the country has granted them.
If you are a legal resident of the U.S., you need to file your tax returns with the Internal Revenue Service and the local taxes that are applicable to you. If you fail to file your taxes, you may be considered to have abandoned your legal status in the country. This will result in the loss of your permanent resident status.
After you become a legal resident, you need to apply for and get a Social Security Number. This number is necessary for tax and employment purposes. If you are a male, between ages 18 and 26, you need to register with the selective service.
With your green card, you can travel abroad and return to the U.S. But there are some limitations. You must not travel abroad for an extended time period or take up residence abroad. If you abandon your legal status in the U.S. and live abroad, you will be stripped off your legal resident status and your green card will be revoked.
The other most important thing you need to do to is to keep your green card up to date. Green cards are valid only for ten years. It is mandatory to renew this card prior to its expiration. Though expired cards can be renewed, wilfully letting the card to expire is not right. As a green card holder, it is your responsibility to keep your green card up to date. By filing Form I-90, Application to Replace Permanent Resident Card, you can get your expired or expiring green card renewed.