So an alexa rating of 12 is good?

Yes, that's right. The lower the number, the better the site. The ranking is based on the number of visitors and the number of page views. Sometimes, you might see a rank for the parent domain, if your blog itself is not old enough to be ranked. For example, let us consider that your blog is on Blogger. If your blog is less than 3 months, normally Alexa will not give any ranking for you. Instead, they will give the ranking of Blogger to your blog. Blogger is currently ranked at No. 12 or No. 13. So, if you do not have many visitors to your blog, then its most likely that your ranking is the ranking of your service provider. Thanks.