How to balance the spiciness in any kind of dishes

First, where you can, use a recipe. This doesn't have to be from a book. If you like a particular dish that you often ate as a child, ask the person who made that dish how much salt, how much peppers, and so on, they used when making the usual amount. (But if you're only making 1/4 as much, make sure you reduce everything in the same factor.)

Second, again where you can, start by adding a little, then later tasting and adding more. There are a few dishes where this is not possible, but not many. For example salt is often added at the end of cooking: taste, add a little salt, taste again, add more if you need to. For some spices that must be cooked first, you can cook up the spicy sauce, but then decide towards the end how much of that sauce to add to the actual dish.

Third, learn how to counteract too much salt, too spicy a dish and so on. There are many questions and answers here about this - the specifics vary dish to dish so I won't try to summarize them here, but they generally involve adding something else to balance things out a bit.

Fourth, keep track of what you try. If you put 8 peppers into a stew and it's far too hot, make a note. Next time try 4 peppers. Over time you'll just remember these things instead of needing written notes, but when you're starting there's nothing wrong with writing things down.