Using view arguments for taxonomy term I have a url structured as such:

http://www.example.com/blog/unimportant-term/taxonomy-term   

(is it a term or alias when the - dash has been added?)

I need to filter my result set based on the taxonomy term, and I don't know how to set that up in my view arguments.

Basically my view is getting all my blog posts, and depending on if there's a taxonomy term present, it will use that argument to filter the posts.
That should be rather easy.  You have to use two arguments, a regular taxonomy argument for your important term, and the global "Null argument" to ignore the unimportant term.  The null argument is added the same way as all other arguments, just have a look through the list.

I assume you know, that you have to set-up a "page" display, specify a path and insert the argument placeholders.