Well, I have been using fish sauce in the same manner that my family has used similar products for as long as I know. A general guideline is that it is used very similarly to soy sauce. I use it in many marinades and sauces, including things like Japanese marinades, soups, sauces (teriyaki sauce is a good target for this stuff). It is such a powerful source of umami, I liken it to the dashi that Japanese use to flavor everything.
But, I also use it in ketchup, BBQ sauce, stir fry dishes, vegetable dishes, casseroles etc...cut out the salt and add fish sauce, it will add the salt, increase the sense of sweetness and add umami. Here is something I highly recommend you try to understand the effect of fish sauce. You use this as a mop or spray while grilling or smoking meats. This kills on chicken and pork.
Pig Honey Sauce
1 cup apple juice
1/4 cup Red Boat Fish Sauce
1/4 cup Braggs Amino Acids
1/8 cup Honey
1 Tablespoon turbinado sugar
Combine all ingredients and bring to just short of a boil, maintain heat until sugar is dissolved. See above for use. I believe it is important not to boil this mixture as I believe the boil process will cause the proteins to denature and not function in the manner I want it to work. I have also become aware of the loss of character that fish sauce can suffer when excessively boiled. I am starting to think it needs to be added late in the cooking process, although I have not discussed this with any scientists. You should end up with something that looks like this