Relevance

It has been said, "For want of a nail, the kingdom is lost".

One of the most potent aspects of this phrase deals with meeting needs.
So too should your blog be satisfying a need.

The challenge, of course, is accurate identification of your niche and its associated lack.

Without knowing your niche, you will not appreciate its scope.
You also will not be able to gauge relevance.

Gladly, numerous tools exist that can offer help.

Too, this ties into tags.

As noted, tags can help your content be discovered.

Tags can also be used to identify the content for which others seek.
In that context, tags are referred to as keywords.