Runes:

A combination of 12 arpen and 14% attack speed for reds and quints gives me good damage and sustain (from warwick's passive). Armor seals and mres per level are good to make warwick super tanky. Optional runes include full aspd for reds and quints, or aspd blues.

Masteries:

I use 21/0/9 masteries for jungling because I like my route to be really fast. Most pros seem to like 14/0/16 or 15/0/15, so just choose what you feel is best. 0/21/9 could potentially work well for late game, but warwick doesn't have much speed in the jungle so you'd be losing out on a lot there. Late game, defense might be good if you wanted to get Ninja Tabi and use Nimbleness .

Summoners:

I use flash and smite. Smite because it's necessary for jungling - stealing buffs and whatnot, despite not being absolutely necessary for warwick jungle. It also makes jungling faster.

Flash is good because you can flash -> ult an enemy champion. This makes for a good initiation on an out-of-position carry. OddOne likes ghost on warwick, however, so it's your choice.

Items:

I start out with Long Sword and 1 Health Potion. This makes my jungle super fast, and makes it so that I can build into madred's razor quickly (less waste on potions). I then build towards my early game core of madred's razor, Heart of Gold, and Boots.

My total build is something like this:

Long Sword
madred's razor
Boots
Heart of Gold
Wriggle's Lantern
Mercury's Treads
Spirit Visage
Sapphire Crystal
Wit's End
Frozen Heart
Randuin's Omen

This is all heavily situational. In a normal game I don't get past Wit's End, so much of that later stuff is just dependent on the enemy and how the game is going. Randuin's Omen is the most situational item of the bunch, and a few things could be bought instead:
Sunfire Aegis good for general damage and tankiness
Guardian Angel good to make sure you can initiate with your ultimate all the time
Madred's Bloodrazor good for more damage
Force of Nature for more MRes
Frozen Mallet helps you stick to your target

I like getting Sapphire Crystal fairly early on because warwick is heavily dependent on mana - much of the reason he can survive in a fight is because of his constant lifesteal. To do this, he needs to be able to Hungering Strike and Hunters Call to get more Eternal Thirst procs. Basically, skills are important on warwick, and running out of mana makes you useless.

I get wit's end fairly late because having that core of tankiness and lifesteal is important so you can actually stay in a fight after you ult. I get wit's end when it's feasible to buy damage without being super squish.

For my jungle route i start at blue, because it opens the most possibilities to me later on and is the hardest to get counter jungled from. If they steal blue, just move on to the superior route. Blue route works best because after you get blue buff, you can jungle really quickly until level 6. The other routes require you to recall too much. With blue route you hardly even need to recall. The main purpose is to get to level 6 ASAP, and even though there's a route for that, it involves making sure your buffs aren't stolen (if they know you don't start blue, you WILL get counter jungled). Once I hit 6 I try to gank a lot, and take dragon really quickly. Counter jungling is fairly easy with warwick, since you can escape with full health, but the problem is you don't have much escapability. You'll have to duel the enemy if you get caught, or flee to an allied lane (provided you don't get caught by enemy laner). Just stick to stealing wraiths and golems for the most part (which you can do after taking your own blue).