I do fanart features. I always make sure to strongly feature the creator's name and the cover of their comic and to give a link to it in the description so that the features actually do give participants a small boost in subs (last feature people said it was about 5-10 new subs) to make it worth their while.
Other than that, rather than tacking on a question, I try to make sure when I plot and thumbnail pages that every update has at least something to discuss or joke about, like a new piece of information about the plot, setting or characters, a joke or some kind of big dramatic moment.