Determine how much time you will be out of the country. The most important thing when insuring the future status of your green card is knowing how long you will be out of the country.
When out of the country six or less months, no extra attention is needed. When gone for six months or less, it is the government's responsibility to prove that you abandoned your home. If you are only gone a short time, it will be harder for them to do so. In most cases, the government will not pursue cases involving six or less months of absence.
When gone more than six months but less than a year, it becomes your responsibility to prove that you did not abandon your home in the United States. You will also have to reapply for admission via United States Citizenship and Immigration Services. When visiting countries that may put you at risk for certain diseases--HIV for instance--the application process may be more difficult.
When gone for more than one year, you must apply for a reentry permit. When your permit is granted, you can travel outside the U.S. until the expiration date on the permit.
