Honestly, the best advice I can give you is to go to university (if you haven’t already; I don’t know how old you are) and take some classes on philosophy and/or writing argumentative essays. And by “argumentative” I don’t mean belligerent or combative; I mean essays that put forward a thesis and support it with evidence and logic. Philosophy courses will teach you how to do that in a particular way, but it’s a more generally applicable skill that might be better served by the kind of classes that teach you how to write, e.g., an op-ed for a newspaper or an online magazine.
In theory, I can teach you, because supposedly my doctoral degree qualifies me to teach critical writing and thinking – though sadly little of PhD training goes toward pedagogy. (I’m designing and leading my own course for the first time this semester and it’s really feeling like I’m a toddler that someone has thrown into a shark-infested lagoon and told to have a nice swim.) But I don’t think I can teach you by myself (certainly not without a lot of work that I’m not willing to do for free). I’ve acquired my ability to write and argue and my basis of knowledge from which to do it over a lot of years of training and practice, with input and feedback and mentoring from a lot of professors in college and grad school, as well as from the PhD students who were my college TAs and were paid peanuts to read my shitty essays and tell me how to make them less shitty. It takes a village, Rome wasn’t built in a day, “stay in school, kids!”, and all those other delightful clichés.
Loki is the Philosopher King 