Get a Reentry Permit BEFORE you go
USICS expects lawful permanent residents to reside in the United States more than half of the time. This is vital in the context of appying for naturalization. However, even if you do not want to be a US citizen, you may endanger your continued LPR status if you stay outside the US too long or for too many trips. If you are planning to be gone for more than one year, it is vital to file Form I-131 for a Reentry permit BEFORE you leave. That may help you return from your extended trip, without endangering your green card. It is not a guarantee however!
Beware of too many trips
If you come back in the US every six months and only stay a few days or weeks, you may also be in danger of losing your permanent residence. See an immigration attorney if this is your plan. You may need to stay in the US for longer periods of time or may need a reentry permit. There are exceptions for military familes, those working for US companies abroad and religious missionaries. If you fall in these categories, see an immigration attorney.
What if I am out of the US for more than one year? Typical Questions on Return
You may be questioned in secondary inspection upon your return. You will be asked to show that you have maintained ties to the US. For example, you may be asked Where do you live? Do you pay US taxes, or are you on a relative's tax return? Do you have clothes, furniture or personal belongings in the US? Do you have a job in the US? Do you own real property or have bank accounts in the US? Where does your family live? Why did you stay away so long?
Should I abandon my green card?
Do you realy want to give up a green card that probably took years to obtain? The Customs and Border personnel may ask you to give up your card and sign a form that you wish to give up permanent residence in the US. They will take a sworn statement. They will probably still allow you to enter as a visitor if you agree to abandon your card, but again no guarantee. Better to be prepared as they will not allow you to call an attorney at that time. If you refuse to give up your card, you will be allowed to enter the US and will be given a date to appear before an immigration judge.
Keeping your LPR Status Before the Judge
You should definitely retain an attorney to represent you in court. That attorney can help you with putting together evidence of your continued intention to be a lawful permanent resident. For example, you can provide tax returns, bank acounts and proof of US property. The judge will want to know why you stayed out of the US so long. Was it due to illness of you or someone you cared for? You will want to provide proof such as medical records for yourself or a loved one if you stayed away due to your illness or the illness of a relative. You may want to present death records of a relative whose estate you needed to settle in the foreign country. If you stayed away to finish a school program, show those transcripts. If you stayed away because you had a job to complete, provide that. The attorney will look a your circumstances and be able to advise you.
Can I refile for a new green card?
There is a possibility that you may be able to be filed for a new green card but that is best discussed with your attorney. If you got your original green card through marraige to a US citiizen or as an immediate relative, that person may be able to file for you again. If you got your green card through diversity lottery or business, you may have no choice but to fight the charge of abandonment of US residency.
Final Thought - Why Not Naturalize?
Although some people should not file for naturalization due to circumstances such as arrests, most permanent residents should seriously consider becoming US Citizens. It will make future travel a lot easier. Best wishes!