If you know Nasus and how to jungle, this should just flow pretty well for you.

With some added magic defense from the runes, and masteries set the way the are you start out with decent defense overall and I go for more with the order of item purchases.

Load up that Q first and if you don't have a leash for red or blue buff, take the dogs out, and just do standard attacks on all three to make sure you farm that Q and get the full 12 stacks from that minion camp. After the dogs, you should have level 2, so grab spirit fire, but do the same for the hissers on the other side of jungle, use standard attacks on two of the small hissers, then cast spirit fire, and get the third small hisser with the q, then cast spirit fire again and proceed to farm q on the big hisser, with this build you should be able to survive the dogs, hissers and the red buff without having the heal or go back to base to buy anything. It will get close for red buff but trust me, with Nasus's life steal you can get close and time that Q just right so you get at least two of the three minions from red buff camp farmed for stacks.

By the time you make it back to base, you should have enough gold for the kindle (early cooldown reduction and added health (plus it builds towards one of your final items), boots, and possibly, if you were paying attention and realized the reason you loaded Wither (w) second, was for early huge slows leading to easy lane ganks/turret takeouts, then you make have enough gold to go for the juggernaut, and if you're really good, even the the ninja boots.

Ok, so now you're all healed and mana is regen'd, look around the map, in case you haven't been doing so already, help out where you can, if its ready for you to jump in, do it, and make wither your foundation, a well played wither can lead to so many things. If you see a gank setting itself up, hit the jungle along the way, you should be strong enough to take out any creep fairly quickly by now. If all is well, just hop back into your jungle, and as i said by now you should be flowing pretty smoothly, and each jungle creep should give you minimum 6 stacks each time you stop by. You have 16 cs in your jungle, and if you time and farm your q right, you can hit 80% of them with it (your q) and get stack'd. You can get all 100% with you Q, but it takes some backing off of minions and timing your hits.

Now that you've got your side of the jungle down, it's time to cross over and take out what's up and alive over on their side. Just cross over through the river. But this time, you should have gone back to base once (or twice) all depending on how much activity you are getting involved in and how much gold you have farmed. If you hadn't by now, make sure you get the juggernaut, and the ninja boots. If you have already gotten those, move onto to the tritons. I like to go with the phage first, it gives you health, atk dmg, and a stacked movement boost upon basic atk.

You get the idea, it's basically, take complete control of the jungle, both sides, and engage with wither as your foundation, followed by a anticipated cast of spirit fire, and you will be racking up the wins in no time.

Try it out, it just works, ya know..