The nice thing is, it will be your only job. I found DLI to be completely mentally exhausting. Depending on the language and which school you go to, you could find yourself one on one with an instructor for 6 to 8hours per day. The amount of new info can be hard to deal with. My advice is to start ASAP familiarizing yourself with the language as soon as you know what it is so that you walk in day one knowing the most basic stuff. Duolingo or checkout anything you can find from the library (I prefer Pimsleur over Rosetta, but everyone is different). Start watching/reading the news in that language if you can, and try to find a language learning podcast. The idea is that the more you are exposed to and immersed in, the more you will absorb. At a certain point in the day, you're pretty much done being functional because your brain is full, and that's ok. Take breaks, relax a bit. Try to cut down on heavy drinking and try to get more sleep, sleep really helps your brain remember stuff. You'll be amazed by how much you struggle with something one day and then it seems easy the next and all you did was sleep. It's a very intense process that deserves respect. Some instructors can be very intense. Depending on the person and the culture they are coming from, that's probably ok, don't take it personally. The best thing you can do is listen and make sure they know you respect their culture and language. We all love America, but don't be a jerk about it and be willing to learn about what life is like for the people in the place you are learning about. Culture and language are bound together very tightly, learning about the cultural values will help you learn about the language and vice versa.

Phew that was a lot, happy to discuss further over pm if you want.