The only mandatory runes in my page above are the armor yellows to sync with your passive lifesteal. Most jungler pages take a total of 12 armor pen (Quints and one Red), but with Spirit Fire you don't actually need any. I still take armor pen quints for extra damage vs champions, because again Nasus' strong ganking point is at level 4, where you'll have 16 pen from runes and masteries, and Spirit Fire will drop the enemy's armor by 20 extra for a total of 36 pen, and the Fire component will also help your ally in lane do damage. I take the attack speed reds instead to simply speed up your initial route, and with them you should have enough health to gank at level 4 without going back to shop. If you're on purple side this is a huge advantage because the enemy will almost never have a ward top at this point.
[imgsmall=skills/nasus/e.png] at level one for quick damage on Golem. [imgsmall=skills/nasus/q.png] at level 2 to maximize your [imgsmall=skills/nasus/p.png]. (Resets auto-attack and procs lifesteal) Max [imgsmall=skills/nasus/q.png] because it's your best nuke, and it is essential to farm it up early. [imgsmall=skills/nasus/w.png] at level 4 for ganking power. At level 8 you need to make the decision to max [imgsmall=skills/nasus/e.png] or [imgsmall=skills/nasus/w.png] first. Maxing E allows you to have the best farming capability, while W is great for ganking. Your decision as to which you max should be based on the enemy's team composition and your team's performance in the game thus far. And a no-brainer. Take [imgsmall=skills/nasus/r.png] WHENEVER POSSIBLE. People underestimate Nasus ultimate a lot sometimes because it's not an instant nuke or a big scary CC. The ability turns you into an AoE Bloodrazor, while giving you TONS of additional AD. This is one of the scariest ultimates in the game in my opinion, and a beefy Nasus shreds enemy teams.
Nasus jungle has become sustained enough in the last patch to the point where he can down entire jungle, from blue straight down to twin golems, without a leash or any assistance. He barely even drops below 200 HP at his lowest point. Of course, taking a leash at blue is never a bad thing. It just means you'll have more health at the end of your path and you can probably gank because of it instead of going to shop. Start with Spirit Fire at Golem. My rune page doesn't quite get you to the armor pen cap in jungle, but that's due to the fact that your E drops 20 armor at rank one. The armor pen quints I use are a luxury for more early ganking damage. Once you have blue buff, move on to wolves. Try to get the last hit on at least two of them with Siphoning Strike. Next, move to wraiths, making sure to focus down the blue one fast. Red can get you dangerously low if you forgot to pop a health potion on wolves (he feels very safe at that point, but you need to keep potions rolling to complete full clear). Before you look to do double golems, look at your lanes. If you're on blue side look at bot. Top lane for purple. Is their lane getting pushed, and the enemy champion has no escape? Flash is easy to make them waste at this point. If not, clear your jungle and go buy boots and two more potions.
In my skill order, I max Spirit Fire after Siphoning Strike. Do NOT do this every game. Deciding between Wither and Spirit Fire is almost purely dependent on team comps. If the enemy has a lot of right click, or no major escapes, then max Wither for the ganking power. Spirit Fire is good to max when the enemy is already safe from your ganks almost entirely (ex: Janna + Tristana lane), so that you can farm and push faster to reach your endgame. Despite not having a gap closer, a red buff Nasus with Wither is amazingly scary. He can perma-slow, and brings a LOT of damage to the table thanks to Riot buffing the base on Siphoning Strike. Whether you should be focusing on ganks or farm is going to rely on how your team is performing compared to the enemy, and the enemy composition. If you can't make a gank happen, don't worry about it. Nasus is still an endgame monster, and farming never really hurt anybody.
Assuming you've gotten at least 75 creep kills on Siphoning Strike, you destroy towers like nobody else. Nasus is an amazing push champion, especially with Spirit Fire doing half damage initially now. Split pushing has always been strong on Nasus, and now it just got better. It will take at least two people to even scratch you before they die because of your ultimate and Wither. If they send a solo person through jungle to intercept you, try to catch them in a choke. There's not many champions that are going to beat a good Nasus 1v1.
Nasus's big problem is his team fighting ability. If you want to team fight with him, you are going to be focused because you have massive damage, and every second your ultimate is ticking you're just going to hit harder. With Merc treads and Trinity, you can beat people in a slowing war, so kiting is not as bad as it was before the Wither alteration. The major thing that will ruin your team fighting ability is snares and chain-stun. Morgana and Lux are a huge pain, and you have to be good at dodging the shot, possibly even using flash to do so. Once you get on a carry, they are going to die. If they opt for the single target stun spam on you, remember that you built tanky for a reason. That should allow for the rest of your team to go unchecked and destroy them. If that doesn't happen, well that's the big problem with solo queue. You can't make your team be good.
The Nasus changes are still fresh, so if you've found something that works better for the jungle feel free to comment. If I agree with it I'll add it in. This is also my first guide so anything constructive is helpful. Hope this information helps you summoners! It's sure working for me.