I grew up speaking english because my dad was english educated. I remember asking my mom what my first word was when i was a baby still learning to talk, sha said;'' it wasnt a word, it was 'i want milk', it was a sentence.'' I grew up with two older brothers and we all spoke english. But this doesnt mean that i am able to speak good english when i grow up, i will still need to improve myself.
To learn a language, first you must understand the basic nature and foundations of it. Reading english novels is a good way to improve one's english, i grew up reading lots of english novels. But for those that doesnt like to read, I recommend watching english movies and english tv series, but while you are watching, enable the subtitles/captions, dont put the subtitles/captions in a language that you are comfortable or familiar with, put it english, this way, you are able to understand the meaning of a word and how to use it. Last but not least, make more english speaking friends and communicate with them using english because english speakers tend to correct people if they use the word incorrectly or mispronounced a word.
So, above are my ways of improving my english. Feel free to ask questions in the comment sections.