When I'm playing Hamelin, if I want to advance with my rats, I'll have three rats walk up a the board, then have the Wretch throw a rat at one, which will activate and become a rat king. (Or if I have two crows I'll throw two rats and skip an activation for the distance; you usually have plenty anyway.)
While my opponent takes their turn, I have a 30mm marker, and I measure where I will move one of my rats and place my marker there. On my turn I move my rat. (Obviously I don't do this if it's going to telegraph something, but it helps me avoid clumping my rats to where they can't spawn a rat king, and helps me plan where the cute little guy will spawn.)
I also use little red cubes to mark which of my models has moved -- I never did this til I played Hamelin but it's very helpful.