Echoing what jens has said series tags are what works and are what search is looking at. Episode tags are often times used either for additional commentary not in the description (or used to before the tag limit) or mentioning the names of characters on the page for people who may have forgotten (I like them).
When it comes to series tags, aside from the main genre/genres you've picked it can be useful to include your subgenre and tags related to relevant things in your comic (i.e historical romance, steampunk, highschool, flowershopAU)
The list goes on for what you can include but it helps to see what others have done for their series