You know the right body language is important for your interview, right? It's an important way to make a good impression. It's all part of the total package that you are presenting to the interviewer: your body language projects a very strong image that factors into the decision to hire you in a big way.
So what can you do?
Expect a positive outcome from this conversation.
The first thing, before you even think about what your arms should be doing or what your eye contact ratio is, is to picture yourself having a positive outcome for this interview. It's much more than a "dream it and it will happen" kind of thing. If you go into it with a positive perspective, your breathing will be more natural, you'll smile, your eye contact will be totally appropriate, and you'll appear relaxed, confident, and enthusiastic. All good things.
Practice relaxing breathing.
Practice slow, calm breathing before you go into the interview. And remember to keep your breathing even during the interview. Calm means confidence.
Now think about your arms, hands, and legs.
You know these. When you meet the interviewer, smile and give a firm handshake. When you smile, imagine that your interviewer is a friend. During the interview, don't fold your arms, or fidget, or touch your face. (And don't take off your jacket, either.) Don't sit down until they invite you to, but once you do, sit up straight and lean forward slightly to project confidence and trustworthiness (it will help with your breathing, too.) And maintain your eye contact in a natural way. Overall, just think "relaxed, but alert."
There's a reason I put those things last. The first two will make the third one easier. And I don't want you to be so focused on whether or not your arms are crossed that you forget to focus on the real reason you're there: to have that conversation, to sell yourself as a candidate, and close the deal to show the hiring manager that you're the person he needs for this job.