1200 Cals/day - what is correct proportion fat/carb/protein

I am committed to losing weight and keeping it off. I started 1/1/13 at 212.4 and weighed in this past Sunday at 185.2. I've been using myfitnesspal to track meals, exercise, etc. I have been doing fine with staying in the 1200 calories/day but would like to know what - in general - are those calories supposed to be comprised of to keep losing weight? Is it 50% carbs with the balance split between fat and protein? Is there a minimum I should be targeting for fiber? How much sodium is too much?