Based off my experiences attempting to speed run N2, I usually recommend spending most of your practice time on reading and next to none on listening.
Listening is some dumb easy stuff. Question are out of four (sometimes three) answers - knock out 1/2 obviously wrong ones and you win that section. Just put some 雑談 streams on while you work so Japanese doesn’t sound like a garbled mess by the time the test comes around.
Vocab/kanji is something you should be practicing regularly, but whether or not you know the words/kanji that actually show up on the test is a complete dice roll imo.
Which leaves reading, I guess. Reading speed (not just accuracy) is very important on the test. The ability to be able to reliably scan is also very useful, but that requires a certain amount of proficiency that you wouldn’t have unless you tried to have it.
I’m not sure if they have it on the N3, but in N2 they give you questions that involve scanning stuff like charts and event flyers - if you haven’t developed the right skills, you can’t do it in a timely manner which takes what should’ve been a free question into something taking time away from the long passages.
Kanzen Master has good reading materials. Alternatively, if reading essays is too painful, you can spend your practice time doing prose (children’s novels etc.). I’d recommend rereading stuff a lot, otherwise you get caught up in all the vocab/grammar you’re encountering for the first time and don’t spend enough time actually developing speed.
Just my two cents