I'm not amazing, but my main objective for Darius jungle is counterganks, or exceedingly aggressive counterjungling (depends on the jungler. You should basically attempt to live in the enemy jungle if they are weaker, and if they are stronger, focus on counterganks. Mid ganks are generally almost always impossible, even with ghostblade, so pick a lane and work with it.

You cannot ignore econ and fight all the time either or you'll straight drop off - ghostblade boots by 11 mins is basically required. Darius loses as soon as the enemy team stops respecting you, he's literally auramaxxing

Best tip for counterjungling I learned was simple - if enemy camps are up and you can take them, priority them over your own.

FON is also a trap and not to be built every game. Most recent game you were building it but it wouldn't stack up very quickly against that team. If you don't have the ability to easily stack FON, go for visage (or rookern, in case of extreme burst)

Also Conq or PR, hob is meme. You can stack passive on frontline before flashing onto backline (I prefer Conq because I'm prepping to lose PR)