There are myriad authors out there with just as many blogs. The ideas of what you can write about are nearly infinite.
They can be spec-fic related, they can be about the trials and travails of an aspiring author, they can be observations on the publishing industry...
One way lots of authors try to build a following is to offer stuff -- free courses, for example, free stories that you've written (and don't expect to see published otherwise).
There are loads of blogs about creating blogs. (Jeff Goins is a popular blogger and author, and part of his spiel is about how many blogs he started before finally discovering how to develop an audience).
My advice is to read other authors' blogs, leave comments. Approach it like you're looking to join a community as you have done here (and welcome!), and learn from their approach -- both what you like about that approach and what doesn't work for you.
Blogging used to be discussed more in this site, but you should still be able to find previous discussions. And if you have questions on those things, feel free to comment on threads even if they haven't had a comment in a while. It kinda brings them back into view. There's so much great information on this site that you can find answers to most of your questions when you're starting out.
Good luck, and feel free to PM me if you have any other specific questions.