I speak fluently with good grammar but it does not mean I don’t make mistakes sometimes or I sound natural, because In my language if i form grammatically correct sentences it’s automatically means I am speaking correctly but that not the case in English language, and I just realized that recently because when I talked to native speakers in my travel they do not correct me so I assumed my English is good but it turned out it’s not ! So when I started asking questions in italki I started to hear from teachers saying your sentences are grammatically correct but they are awkward and does not sound natural. So there is no rules to follow but to copy how native speakers talk, Luckily though I am Mystique and copying others is my forte !