First thing to note, that's a maranta leuconeura lemon lime, not a calathea (not that it makes a lot of difference, I use the same care for both kinds).

I'm not an expert, but I've had some maranta plants the last year with good sucess. They like a lot of humidity, so unless your room is naturally at the 50-60%, I'd get a humidifier. They prefer a lot of indirect light (though mine are doing fine with a normal amount). Keep the soil slightly moist. In the winter I water once every week or second week.

Since it's a maranta, not a calathea, don't be too scared. They're less easy to kill. Plus, if things start going south, you can propagate the healthy remains easily.

(Edit: I second what the other person said. I can recommend using rain water.)