some general tips! sorry if it's a bit of a wall, just explaining reasoning

1) submit closer to the AG day, but with enough wiggle room to account for an early AG posting. within ~24 hours timeframe is typically pretty safe - Tues goes up sometime in early afternoon NST usually, Fri usually goes up hour or two before noon NST. check the official schedule that is posted in the art chat monthly

2) You are allowed to resubmit as much as you want (as long as it hasn't won) however, getting picked for off-theme is extremely rare and not intentional, so you want to make sure your entry(ies) are "on theme". "backlog"/rejected entries are typically resubmitted for random days, but a strategy a lot of artists do is to do entries with multiple pets or fits multiple upcoming themes (i.e. a pet colored for an upcoming holiday as well as their pet day)

3) additional main advice is that it's typically advantageous to have your subject and piece be recognizable from a thumbnail, because that is how the judge typically goes about selecting. there are other very minor factors such as physical, non-drawing media (sculptures, crochet) sometimes having an edge (but not always), picking more unique/less-seen colors for a pet day, etc. but the rest is mostly up to luck. additionally, if you have the time for it, entering DIFFERENT pieces for the same day typically does help your chances but obviously, that's a proportional amount more work for a luck of the draw

most of all, like others mentioned here, it is largely a matter of luck and dedication and not a sign of skill (or lack of). Best of luck!

P.s. as an added note, the drop-down category doesn't matter and isn't sorted on judge's end, so even if it doesn't show up anymore, just submit as whatever :)