If you're not sure, then try playing games and voting on them when the games are released (Oct 1). Then when voting is over you can say "Wow, I can totally do better than some of those" and think about writing a game for 2019. End of public service announcement.
(Last year I livetweeted the IFComp results and probably got myself blocked by everybody on this server. La la la.)
@aggsol Excellent questions! The comp comes from a hobbyist-videogame history; the videogame format is an unspoken assumption in the rules. People have entered game-book-style PDF documents (http://ifdb.tads.org/viewgame?id=juj5b61griyoswn2, http://ifdb.tads.org/viewgame?id=3hxnnssx2ubid2t2). It's clearly accepted but we haven't gone out to those communities saying "You should be in IFComp."
@aggsol Really this is the first year that we've talked about outreach at all. My tweets/snuffleupagations are a first attempt at doing that. Historically we've been reactive rather than active -- a lot of Twine games started showing up five years ago, so we said "Okay, I guess we're a comp that has a lot of Twine games now!"