Use tagtastic's shop stats to see how effective your current tags are. After plugging in your shop name, you can scroll down to see a graph of your tags with the most views per day. Further down the page you will see a list that allows you to sort your tags by average views per day, average price, and number of items with that tag. Pretty useful!
Are you like me and struggle to fill in all of your tags? Well, one way to use Tagtastic is to enter a theme or category in the search field. Then, when you get the results, go down the page to related tags and sort by 'number of items'. You will then see the tags that are most often found with the tag you searched for. Using those tags with the highest views from the table will increase the number of views your item gets daily.
Tagtastic provides a lot more information than I've mentioned here. It is worth taking a look and doing some exploring: