First off i would like to say that this is not an finished guide and you might benefite more from other guides but, nonetheless, i feel i have some knowledge of Darius worth sharing.

Hemorrhage - Darius aims his attacks strategically, causing his target to bleed for 12 / 15 / 18 / 21 / 24 / 27 / 30 / 33 / 36 (+0.4 per bonus attack damage) magic damage over 5 seconds. This effect stacks up to five times.

Darius gains 5% movement speed for each bleeding enemy champion.

Decimate - Darius swings his axe in a wide circle. Enemies struck by the shaft take 70 / 105 / 140 / 175 / 210 (+0.7 per bonus attack damage) physical damage, while those that are struck by the blade take 105 / 157.5 / 210 / 262.5 / 315 (+1.05 per bonus attack damage) physical damage.

Crippling Strike - Darius's next attack severs a crucial artery, dealing 20 / 40 / 60 / 80 / 100 % additional physical damage. As the target bleeds out, their movement and attack speeds are slowed by 20 / 25 / 30 / 35 / 40 % for 2 seconds. Crippling Strike's cooldown is reduced by 1 second for each stack of Hemorrhage on the target.

Apprehend - Darius hones his axe, granting him 5 / 10 / 15 / 20 / 25 % passive armor penetration. When activated, Darius sweeps up his enemies with his axe's hook and pulls them to him.

Noxian Guillotine - Darius leaps to an enemy Champion and strikes a lethal blow, dealing 160 / 250 / 340 (+0.75 per bonus attack damage) true damage. This damage increases by 20% for each stack of Hemorrhage on the target up to a maximum of 320 / 500 / 680 (+1.5 per bonus attack damage) true damage. If Noxian Guillotine is a killing blow or the target dies within 0.5 seconds after use, its cooldown is refreshed.

Your core items are Mercury's Treads, Phage/ Frozen Mallet, Madred's Razors/ Madred's Bloodrazor and Maw of Malmortious. In addition to these items I have listed Sunfire Aegis and a Bloodthirster

Even though some may argue that he is not a good jungler, I, personally, find him more then viable. Due to his two great CC spells, Apprehend and Crippling Strike, his earlygame (and lategame for that matter) ganks often result in kills.

If you have a proper rune-page and such jungling will be no problem. You can start where you want and do not necessarily need a pull.
I, however, often start at redbuff for then to do a early level 2 gank at the nearest lane (depending on team)

I have seen some other jungling Darius'es and they tend to use Decimate instead of Crippling Strike.. Crippling Strike is the superior jungling skill for multiple reasons.
First of all, when you have applied your 5 stacks of Hemorrhage the CD of Crippling Strike is reduced to 2sec, which makes it almost spammable. Second of all it reduces the monsters Attack speed, and since you can apply it so often the debuff is constant. And last, but not least, it is far more viable in those level 2 ganks.

Noxian Guillotine is commonly refered to as an "last-hitting" ultimate. And many people tend to use it in similar situations as one would with Garen's ultimate Demacian Justice and Riven's ultimate Blade of the Exile. But unlike their ultimates you do cant just hang around and wait for the target to get low. You need atleast 3 stacks of Hemorrhage on an enemy to best utilize its potential.