First and foremost, you don't want to get ripped off. You don't want to sign a contract which signs your rights away, gives up creative control, or gives up your intellectual property rights. So, be careful for any terms which may do so without appropriate compensation.
If they're paying you money to make this game you've prototyped, you should also keep in mind that you may not want to work on this game as a solo developer. You may find that a few months down the road, you need help in areas that you don't have a good skill set in, or you just have too much work for one person. This means hiring someone to work with you and that usually equals paying wages and that means you have to have a place for them to work, and that comes with some slight facilities costs. Whatever happens, you'll want more money than you personally need due to unforeseen cost overruns or future expenses.
That being said, since you're dealing with someone who you've never done business with before, you can't necessarily trust them. Especially as an international relationship. The simple response is to agree to some contracts, but what happens if one party breaks the terms of the agreement? How are the contract terms enforced in international law setting? It would be easy for someone like you to take the money and just disappear without a trace and there's very little legal recourse. Or, you could sign some agreement where you deliver a finished game and expect to get paid for it, but never do. I think, in a scenario like this, what would probably work best is some sort of milestone payment system, where you and the publisher agree on a set of milestones for the project, and you get paid each time you reach one. And, to get things started, you'd need some seed money both to start working and as a sign of good faith and commitment on behalf of the publisher.
Keep in mind, every publisher is treating your product as a risky investment. They want to make money off of it to recoup their up front costs, so you're going to get pressure to monetize the game. You'll have to explain to them how you plan to make money off of this, and if you don't, they'll plan it for you (and you may not like their monetization strategy).
Anyways, take my words with a heavy grain of salt. I've never worked with a publisher myself since I'm independent. But these are things I'd look out for.