As with any skill, there are specific quick hacks you can apply to get a lot of gain really fast, and there are well-worn paths that you should travel to maximize gains and minimize time spent. Regardless, the best way to learn any skill is through sheer practice.
My methodology for posting comments on HN or any social news site is based on my values. I value production over consumption, and so to curb my consumption and increase my production I created a rule for myself: If I read a post on social media(HN, reddit, etc), I have to leave a comment on it. No ifs ands or buts. I almost never actually want to comment, but by the time I'm done commenting I'm always glad I did.
This is amazing for becoming a better writer and researcher, and forces you to dive into things that you normally would only attain a surface-level understanding of.
Every time I decide to go to a social media site, I have to be very conscious of the titles I click on to read. I understand that the moment I begin reading an article, I am committed to adding something of value to the discussion. Sometimes I wind up clicking on an article that is way out of my domain-knowledge, and so I have to read WAY more about it before I can even try to add to the discussion. I end up learning far more and also upping my ability to explain and present myself in situations where I'm uncomfortable with the domain.
So while I encourage you to practice your writing, I also encourage you to limit your consumption, strongly link your consumption with your practice, and most importantly, step out of your domain knowledge and never be afraid to learn something new.