The Importance of Theory in Linguistics

Theories are self-contained units. As long as you follow some theory that you're comfortable with, it's going to lead to a certain amount of structure in your conlang. Most theories applied with a little bit of care will get you a realistic language. They might bias you in certain directions, but they will. However, you do have to watch out. And when you're reading about these theories, pay attention to places where they're trying to describe real languages.