How do you decide what to post about?

I have started about 10 different blog entries in the past two weeks and all have been dumped. One was slightly negative and I thought it wouldn't be great to make my blog into a place where I can complain about daily happenings. One was about all my great thrift finds and I scratched that because I didn't take a picture of it all before placing the items in their proper homes. The last was on the joy of parenting and I'm not sure why I tossed that one but I did. I was also mapping out an idea in my head on being a step-parent of a late-teen year old. Looking through my posts it would seem to be that my blog is about blogging.