It would be great when tags can be grouped per category. I.e., when one selects category SEO he will be shown tags such as link building, whitehat, content marketing, etc. When posting a question in another category, he will be shown different tags to choose from. I.e. category coding he will be shown tags such as PHP, HTML, CSS, etc.
These tags should be visible in the screen right after selecting the category, by stimulating people to select the right tags.