Like any food or beverage, it’s best to start with a basis recipe. Get good at it; be familiar with it. From there, you’ll recognize it needs more of something, or less of something else.
Think about making chocolate chip cookies. You have a base recipe, but think it needs more chips; so you try to double the chips, and realize that’s too much, so next time try 1.5x the base recipe, keep tweaking until it’s what you want. Here’s the rub, suppose you’re a real chocolate junkie. You may come to the point where you see if you put in the amount of chips you really want, the rest of the recipie simply can’t hold together. You may get the same with beer recipes.
For homebrew, keep detailed tasting notes every time you make a change.
After about 10 brews of your recipe, you’ll either have it perfect, or realize you’ll never think it’s perfect, and just settle on an ingredient list, and maybe come to an understanding that you’re your own worst critic... ...or maybe that’s just me.