When I start my posts, I usually start with an idea. It is just one thing that may have touched me throughout the day, a thought that went through my head, a quote, or a simple event during the day. But just because you have one thought doesn't mean that you can write an entire post about it. I guess what usually happens is that one little piece kickstarts the rest of the post. It will wander and go places that I never intended to, but that's totally okay.
My boss often talks about writing books this way. I'll ask how the writing is going and how the story is going and he'll say he's not sure what's going to happen next. In the most simplistic way, basically he puts the characters in a situation and just lets them react. As long as you know your characters beyond slight acquaintance, you'll know what they would do in the situation.
However one of the hardest things I find about blogging is putting a title up there. Sometimes I don't know what to write. Sometimes I want to just leave it blank. Often is I'll mold the idea that I had into some semblance of a title, that supposedly explains in a phrase what the entirety of the post is about. But how is it even possible to condense an entire lengthy post into a few words? With the utmost concise clarity is probably a viable answer.
I do think that the important thing to remember here is that the title does not have to fully dictate what you are writing about. It's your blog and your words, and if it wanders off the beaten path a bit before coming back to the beginning, so be it. In fact the deviations from said path are often the most interesting part because they are the sidenotes, footnotes, and added thoughts by the person writing. They are the pieces that the person will chuckle to him or herself while writing. Or something that popped into their mind that they wanted to share.
Of course, if you run a blog that is centered around a specific topic, you sort of have to stay within some boundaries, and maybe even all the stuff I just wrote down is all null and void.
At the end of the day it all comes down to your style. You gotta do you, and some people start with a title, some people find it halfway through, and some still struggle to find it at the very end (fun fact: the same thing happens when you're writing songs!). So what's your style? How do you write? Feel free to share in the comments.