Suppose that your favourite character (or least favourite) from the final season of the show got sent back in time to the first season of the show, and met themselves. What would they say to their earlier incarnation? What warnings or advice would they give? What questions would their younger self most want to ask? For that matter, what would each version of the character think of the other? Would they be surprised, shocked, pleased, disappointed, proud, ashamed, flabbergasted?
My own answers to this, dealing with Buffy, are here. Although I took the approach that I wanted to stay canon-compliant (or, in the story, future!Buffy didn't want to change her own past by being too obvious about her warnings and advice) so she was cryptic and elliptical. I'd be interested to see what other people come up with!