i wanna read this but idk where to start

if you've just watched small snippets in every season then start from the very beginning.

thing is I've watched a few episodes of season 1 so do I continue where I left off or just go to the very beginning

I think you can continue from season 1 > jjk movie zero > season 2 > jjk movie shibuya inccident (the fighting scene is insane in this movie and more like recap from season 2 but the story continued to season 3) > season 3 (still running, episode 5) (=・ω・=)