Can my Green card be taken away from me?
Yes, you can lose your green card. If you are gone out of the US long enough to have a customs official make a determination that you don’t appear to reside in the US, he/she may block your entry to the US. That is the reason why it is so important for you to apply for and receive a re-entry permit when you leave the US for any extended period of time. You can be deported from the US for committing a violent crime. And you need to inform USCIS within 30 days if you change your address.
I need to travel out of the US for more than a year. Is there something I should do before I leave the states?
Yes, you need to file for and receive a re-entry permit. That shows the customs official on your reentry that it was your intent when you left the country to return. If citizenship in the US is your goal, you need to be sure that it “looks like” you intend to reside here.