It’d be nice if there was an animated GIF, bold and large at the top of the page, with a Vote for One ballot. It could then slowly transition to “Vote for one or more” with markings on multiple candidates. For added effect, let the viewer click on ovals to mark candidates and try it out themselves, as wolftune suggested with star.vote
Also, I want to point out that approval.vote’s main video (https://www.youtube.com/watch?v=db6Syys2fmE) has a flaw: it features a nice, blue, female candidate beating an old, orange, male candidate with the help of Approval Voting. Seeing all the negative comments from Trump voters reinforces that subliminal feeling, I think.
Finally, it’d be nice if we had even more materials highlighting that Approval always lets you vote your favorite. That’d be a huge win for getting 3rd party supporters and protest voters (“I wanted to vote for Bernie but had to pick HRC in the general”) on board, though it will run into “I wanted to express greater preference for my favorite!” issues.