But my biggest bug bear is the amount of time is sucks up to create something.
Yes, it is mine too. Batching blogs (writing several in a row and scheduling them to go out over several weeks/months) can help. My other trick is guest posting/author interviews. They do the bulk of the writing work while I do the loading and promotion. It means I'm able to have fresh content on my blog most weeks.
What makes a good, effective post?
Lots of things! Listicles (i.e. 10 things I learned while writing my first draft) and how-to guides do quite well. People also love personal experience stories and stories that give a peek into the creative process. For me, I love learning about the stories behind the stories. What inspired a certain scene, where the idea for certain characters came from. Now I think about it, I should go listening/watching the questions people ask authors at a few conventions to get some more blog ideas.
Blogging: I wish I’d known ... that what you think you’re gonna do at the beginning (and how often you’ll post) is not what you end up with once it’s got going and you’ve got more experience.
Yes, 100% true. I started off ambitiously thinking I could blog once a week around FT work and my projects. Then that became once a fornight, then once a month, then not for a while (before I started interviewing authors to get it rolling again).
Why can't I work out how to have different thread headings on my blog and write as if it;s my site rather than adding by simply commenting to myself.
It's an SEO thing and also an accessibility thing. Most blogs will have some SEO basics built in e.g. the title of your blog is always a Header 1 to help readers, screen readers and web crawlers know, roughly, what the topic of the content on the page is. I'm fairly certain blog comments don't show up on search engines or if they do, they rank very low down the list. So, say you wrote an amazing post about worldbuilding in a comment on a blog, search engines wouldn't pick it up. All that work wasted! Readers are also unlikely to look for additional full length blog posts in the comments and it could also be a bit jarring if the original blog title has nothing to do with the comments that follow.
if i can't do my blog properly, does it even matter if no one finds it?
No, not really. It comes back down to purpose. What do you want the blog to do? If you're just wanting to give it a go, trial a new medium, new writing styles etc, and aren't interested in getting viewers—at least not at this point—it doesn't really matter what you do*. Posting a blog doesn't automatically get you readers (unless you're a celebrity or have a website that already has high traffic). The only way people will find your blog is if you promote it (or by accident, and even then its pretty unlikely). So the upshot is, you can experiment as much as you want
*Caveat: until an agent comes to look at it.