How do you define the success of a blog post?

There are several ways to define the success of a blog, the most traditional and cliché ones being the quantitative methods, such as the change in the number of visits, average length of stay on pages, subscribers to feeds, non-spam comments, interactions and sharing across social media, etc... The other -and not less important means- to measure the success of a blog post is the qualitative aspect, that is the quality of the post content, its originality, appeal and relevance to the target audience and the blog's context and objectives.

Both aspects are equally important for a successful blog post. As an example that quantitative alone does not do, take posting a funny video about a baby on a cooking blog. The video can be so funny and appealing that it will indeed garner wide attention and high statistics [quantitative success], but qualitatively, this post is simply sharing the work of others [which could be fine many times on a blog] alas, it is not related to cooking at all. Sharing as such is meant for social media accounts and not for blog posts. That is where the qualitative comes into place. Yet, as an example on how qualitative alone is not enough, imagine the same blog, but with posts that are about cooking, new recipes, techniques, original content, images, etc... but with no exposure or sharing. Such blog posts even though being of high quality and relevance cannot be said to be successful, because they are not reaching any one.

I hope this will help.

More the Visibility On1st Page- More the readers to comment on - More the chance to succeed .

I think the term is not SUCCESS, but VISIBILITY because when we do blogs, we primarily aim for more visibility - and eventually - traffic into our website.  We can say that a blog post gets greater visibility if it lands on the first page, or on top of the first page of the search engine results page (SERP).  Another thing that indicates good visibility is when you receive several feedback from users, or when there's growth in sales of the products/services you're promoting.