First of all, you have to know that Pad Thai Sauce is a combination of four flavours which include optionally spicy (cayenne seasoning or other pepper), sour (tamarind paste or lime juice), sweet (sugar) and salty (fish sauce, soy sauce or salt). If you live in Asia, you can find all these ingredients easily in the stores. However, you may have to search some stores for it, if you live in some other continent.
After getting all the ingredients, you have to mix them well. Even though, there is no standard way to mix the ingredients, however, you can start with two tablespoons of fish sauce, then add two tablespoons of sugar. After that, add a half tablespoon of tamarind and one tablespoon of cayenne pepper seasoning which is optional.
Mix all the ingredients well with each other. Then, keep the mixture in the microwave for just about 30 seconds. Get it out of the microwave and stir it again lightly and taste it. If you think there is a need to add few things, you should add them at this point in time to make it taste better.
Now, your Pad Thai Sauce is ready and you can use it to prepare any of your recipes. You can also store it in refrigerator, but make sure that you put it in a safe jar and cover it well.