Applying for a green card is necessary for securing permanent residence in the US. If you've gone through the process and already obtained a green card, congratulations; you've surmounted a major obstacle to remaining and working in the country. However, as a green card holder, you still remain vulnerable in multiple ways and need to safeguard against losing your status in the future.
Proving your intention to remain in the US
If immigration officials have doubts about your intention to reside permanently in the US, you might lose your green card. One example of such a situation is if you begin to live for lengthy periods of time in another country. It's not enough to make sure you do not stay outside the US for more than 6 months straight and the return to the US for a few weeks or days each time.
One general piece of advice for showing intent to reside in the US is to apply for a reentry permit if you're planning to leave the US for more than one year, but less than two years. However, even if you're leaving the US for less than one year, you might still come under suspicion for having abandoned your permanent resident status. To strengthen the case that you wish to remain a permanent resident, you should have a valid US address, open and maintain a bank account in the US, and correctly file income tax returns, even when you're abroad. If need to go overseas for some length of time, document the reason why; for instance, if you're abroad for business reasons, keep a handy copy of your employment contract.