Further to the credit rating thing, I'll post something I wrote for a friend. Note that you can only do this if you have been issued a social security number.

If you're planning to stay here more than 2 years I highly recommend building up a credit rating. It's a pain in the ass, but so many things in the USA depend on your credit score. It's absolutely insane, but that's the way they do things here.

You can actually build up from scratch, even if you can't leverage your home country credit rating for a boost. To start, you can get a secured credit card, which requires a cash deposit. The bigger deposit you make, the bigger your credit limit. Your current credit limit is something banks look at when you apply for a real credit card, so it's best to get the secured card as high as you can and then a year later get a normal card (or just keep it small for a year, then get it increased by putting more money in, wait a month, and then apply).

Once you have enough credit on credit cards (5-10k), you can start getting other kinds of loans. Diversity in loan types is looked upon favorably. I used this trick in Canada to build my rating up there, basically taking a car loan and then putting the cash I would have paid into a term investment that yields a higher interest rate than I'm paying for the loan. I was going to do that in the USA as well, but they only give loans for cars that are less than 15 years old :(

When you first start out, you'll need to build up a history of about 2 months with your bank of having used your card AND paid your card. Once that's done, they'll have reported your activities to various credit reporting companies like equifax and transunion. Next, you can write to these credit reporting companies to request your free credit report. They'll send back a request that you prove your identity, asking for copies of various identifications, which is a bit of a pain, but you only need to do that once.

You should also make sure that your SSN is clean. When I first came here, I couldn't get a card, and I just assumed that it was because I'm a foreigner. It turns out that in 1994, someone had opened a credit account using a fake SSN. When I arrived here in 2011, I was assigned that compromised SSN, and it took me 2 years to clean everything up. My record is now clean, but I never would have known if I hadn't inquired about it with the credit reporting agencies and the bank. I could have had another 2 years of credit history by now if not for that.

Here is what affects your credit rating:

Credit card utilization (high impact): Keep it below 30%, but always above 0 (having zero credit utilization is bad). Just don't carry a balance. I always make sure I spend at least $10 each month with the card so that it never goes to 0. Also, when I had low credit, I would make a purchase, and then immediately go online and pay off all but about $10 of it.
One thing to note: This factor is only affected by the previous month, so it's easy to fix.

Payment history (high impact): ALWAYS ALWAYS ALWAYS pay your card on time! I set up an automatic payment system with my bank.

Derogatory marks (high impact): Only affects you if a company sends a collection agency after you and you don’t pay up immediately when they call. Derogatory marks fall off after 7 years.

Age of credit history (medium impact): You'll get hit hard with this, as I am being hit now. You need 9 YEARS of history to get an excellent rating here, and 2 years just go go from "very poor" to "poor".

Total accounts (low impact): This one is just stupid. Basically, you need to have 6 credit cards just to go from "very poor" to "poor".

Credit inquiries (low impact): You get fucked on this one all the time. Everyone under the sun will do a hard credit inquiry, and they'll usually trick you into saying yes without actually telling you they're doing it. Others will just do the hard inquiry without even asking you, and even though that's illegal, they get away with it. I currently have 14 hard inquiries on my file from phone companies (they did 3!!!), comcast, alarm companies, banks, basically any company that will be billing you monthly. You can have max 2 before it affects your rating much. After 1-2 years the inquiries fall off, so if you're doing anything that will likely cause a hit, it's best to do them all at the same time (sometimes if they are within a week of each other, they'll end up only counting for 1 inquiry in aggregate).

Total credit (affects how much more credit you can get): The more credit you have, the more they are willing to give when you ask for it. The higher your overall credit limit, the more favorably companies will see you.

You can probably build your rating up to the low 700s within a year as long as you're careful. Anything 680 and above is looked upon favorably when trying to rent an apartment. I use a program called "Credit Karma" to help track my credit rating. They also have tips for optimizing your score, but basically it boils down to what I wrote above.

Oh, and one last thing: Once you get close to 700, you’ll start getting credit card offers in the mail. Many of them will be “pre-approved”, which is a baldfaced lie. If you reply to them, you’ll actually be giving them permission to do a hard credit inquiry on you, and you could still end up being denied. It’s best to do your research and pick and choose your cards. I always go for cards with no annual fee, even if they have high interest rates (which don’t affect me because I always pay down my cards at the end of the month). Another good thing to look for is point systems. Most of them are 1 point per dollar spent, but some of them have introductory offers where, if you spend a certain amount in the first 3 months, you get a bunch of bonus points. I do this with companies that allow me to trade points for $0.01 each. Last year I waited until I had a bunch of expensive purchases lined up, then got the card, then immediately bought those items. It worked out that after cashing in the points I got 25% of my purchase cost back (spent $2000 to get the bonus 50,000 points, then cashed those in for $500). Lots of cool things you can do with these special offers so long as you are disciplined in your approach.