Add steam id tag and some tags like "official cover", "fan cover" and others. I plan to write utility for updating steam with these covers.

Some tags so far:
fanart
anime
textless
no_logo

Also for game titles you can tag as "foo_bar_baz" but I think also tag as foo bar baz leaving out common words.
Booru.org doesn't seem to cap search terms so it makes it easier to search games without having to know the canonical tag for example tes,morrowind,elder,scrolls vs the_elder_scrolls_III_morrowind or whatever.