I would say a good first measure of good content would be once you get done writing a post, would you feel comfortable telling people that you've got a post that they MUST see? If you don't feel confident enough that someone will find it important, go back to the drawing board. If they ask why they must see it, do you have a good reason? If not, back to the drawing board. It's all about creating content that people will find valuable. You need to say something that will make a person stop for a moment and take interest in your words. Maybe it's because they are learning something, maybe because they are captivated by your story. A good way to learn some of the techniques you can use to create good content can be found on
Copywriting tips for online marketing success from Copyblogger (plus most of the posts I've read there could be considered 'good content' as well).