I learned two things, mainly, one from the feedback on my game and the other from looking at the other submissions.
The first is that no matter how obvious I think a concept is it has to be clearly spelled out in the game instructions or a tutorial or an on screen prompt or better yet all of these ways. Same goes for the commands, no matter how intuitive I think they are.
The second is that unless it's impossible there should be a properly functioning web build, with the right resolution and all the features working, and well thought cover image and game description: in the last two days of the voting phases I filtered the submissions to only show those playable in browser and picked the ones with interesting covers.