How Did You Get Good at Your First Language?

People have a hard time accepting that even when you do sort of explain it to people who are learning their first language. It can be really hard to shake preconceived notions. Part of the thing that excites me about learning a language as a fully fledged adult is just how conscious I get to be of the process, which is something bilingual or multilingual people that learned languages from really early age don't have.