HN in my perspective, is mostly a PR site for technologists trying to push their brand/personality with some bigger agenda.
I've seen a lot of people develop their brand/persona on HN and blogs before trying to push out some tech company. 3 such people come to mind.
To be fair, I'm probably no different, except that I dont post here (yet) -- just consume and opinionate.
So consider the context.
If you really want to be good at writing the best way is to practice. A blog is a great way to get in the habit of writing.
I would also refer you to some well known books like the de facto standard for "good" English composition used by PR's and news organizations: The Elements of Style (http://goo.gl/SPcAOF Like anything they key to becoming "good" is time, focus and dedication -- obviously.
In any case, consider the context of HN and what the motivating factor is for people who do submit posts here -- they write well because they have an agenda and are using language as a tool to advance their agenda -- me too!
(side note: I'm still trying to figure out what the motivating factor is for Redditors though, if anyone knows, please let me know.)
(side note 2: I'm really surprised that in the book mentions, no one mentioned Elements of Style - it really is a big deal. Ask any Literature/English professor. I just re-ordered it myself for nostalgia sake and I'm always catching myself trying to remember the rules from it)