Hi Hannah7,
Like Jackolantern said, you have to prove that you were just temporarily outside the US and have established residence. So, you should do some things like get a driver's licence, maybe a credit card, if you can, open a bank account, etc. You know, stuff that you would have if you were actually living here, but which you don't have to waste money on if you're going to Europe for 10 months (like a cellular phone contract). However, you could, if you have relatives or good friends in the US, have your name included on a lease or the ownership title of a car, or even get something like a cellular phone contract in your name but have your friend or relative use and pay for it. These things may help you in the future.
I'm a student in Amsterdam, too, and I have a GC (by the way, just out of curiosity, where are you from and where are you studying?). I have way more ties to the US because I've been living here for more than 10 years, but my mom includes me in a lot of her stuff, such as credit card accounts and the title to her condominium, so that will help when I apply for citizenship later on.
As for re-entering the country, you should be able to explain yourself. So, having such documents on hand would help in case you're sent to secondary inspection (just a little room where they question you further). Also, have some letter from the university proving you're there just temporarily. An end-date for your stay abroad is always good. I have an RP (Re-Entry Permit) now, but before, I traveled on an RTD (Refugee Travel Document), so I've had fewer problems, I think. They've never been too suspicious of me. I was out for about 5 months, came back for 20 days, and left for another 5 months. Now, with the RP, the IO hardly looked at me (which is good). So, I think an RP DOES help. Yes, it's a lot of money, but your GC, in my opinion, is well worth it. Just consider the expense as part of your GC fees (Diversity lottery, right?).
Good luck