Hello and welcome to my first MOBAfire guide. This guide will explain both basic and advanced Nunu jungle strategies/tactics. This guide, like Nunu himself, is flexible. If you have any ideas of your own or suggested improvements be sure to comment about it!
I see Nunu as an underused jungler in ranked and I am writing this guide to hopefully spread the yeti love.
Before I continue, I'd like to take a moment to introduce myself. My summoner name on North America (NA) is: Ree Sing (I recently changed my name to this as a bit of a pun). I main jungle but also enjoy playing solo top.
Keep in mind this is my first original MOBAfire guide which I will be updating often, if there are any suggestions, constructive criticisms or simple feedback on how I could format my guide better, please feel free to leave a comment! Also, if this guide worked for you, a +1 would be most appreciated.
Now that the boring stuff is over, let's get into the guide.

Pros:

-Amazing sustain in jungle with consume.
-Ultimate can be deadly when used correctly and can flip a game.
-Tanky, with some great utility (W+E+R).
-Amazing AP ratios on Q, E and R.
-Above average Crowd Control (CC).
-Counter jungling/invading made easy (Q+Smite).
-Early dragon control with a co-operative bot lane and Q+Smite.

Cons:

-Ultimate is easily interrupted with any form of stun/silence/suppress/taunt.
-Slow movement speed until you buy your tier 2 boots (Blood Boil helps).
-Relatively low clear speed in jungle until level 8~10.
-Hard to gank a lane with stuns.
-Annoying voice actor ruins badass yeti noises.

This is the most flexible part of how to play Nunu.
The suggested items above I have are a solid build, making you survivable, sustainable and giving you a damage/disrupt boost. There are many other viable items to build on Nunu and in the near future once I've finished my Lee Sin guide I will go more in-depth on which items to build on Nunu and which ones to not. I'll explain more about my thoughts on choice of boots and have a whole section on aura items, but for now the suggested item build up the top of this guide will have to suffice, sorry.

The runes I use on my jungle Nunu are effective thought unorthodox, but suggestions are very welcome.
The runes aim towards:
a. Early game beefiness (health)
b. Late game sustainability (health+magic resist)
c. A small but vital AP boost early which gives you damage and sustain when ganking and jungling.

Why health?
I get this question all the time, and I can honestly say, health is an extremely important stat on Nunu. Health increases durability in team fights and sustainability in jungle (more early on). With this guide, unless you need to adjust the standard build (situational items), you will end up with a strong 3350+ hp. How does this give an advantage to the team? With this build Nunu is a sustainable, tanky AP bruiser with great support (W) and sustain (Q).

Some Nunu players like to go flat AP and pretend they are a utility caster like Viktor, but in my experience these runes are the stronger and more balanced choice between tanky AP and AP caster in ranked games.
If you're in a normal with buddies then by all means play AP Nunu and have a laugh. :).

My mastery choices for jungle Nunu focus on early game strength when ganking and in the jungle (reducing damage taken/reducing damage from creeps) which scales decently into late game with health per level. Honestly, mastery choices are extremely based on personal preference and if you feel more comfortable using different masteries than the ones suggested in this guide, feel free to do so! By all means, feel free to comment with mastery suggestions or improvements!
This is the way I like to set my masteries up, but if you prefer anything different please let me know, thank you.

The summoner spells I have suggested for this build are Smite+Ghost. The most frequent question I get about running these spells on Nunu are:
a. Why Smite when Nunu already has consume?
b. Why not flash? It's better than ghost!

Why Smite?
You're jungling, yes your Q does true damage, but most of the time it just isn't enough to control big map objectives like baron or dragon, which as a jungler, is a big part of your role. Just take it, when your team gets baron and pushes to the enemy nexus you'll be thanking me.

Why not flash?
I take flash on almost every champion I play. It's a perfect spell, sometimes better than Ghost; That being said I prefer Ghost on Nunu because it allows you to reach fights easier, chase, escape and even disrupt enemies.
Sometimes I take flash on Nunu, sometimes I don't, what you do is totally up to you!

Another question I get but not as much is "why don't you take heal instead of smite." While some junglers take heal, I see it as foolish, you either not out your smite secure or your escape/chase for a bit of hp. Nunu already has his Q and a tad of spellvamp with this build. You simply don't need heal.

There's really not much to talk about here, the order in which you level Nunu's abilities in jungle should be fairly obvious.
Taking Q first and W at level two are necessary, but afterwards, the skilling process is a bit more flexible with the exception of having to max your E.
Put simply I max Nunu's skills like so: R > E > W > Q

Literally a piece of cake with Nunu.
Your Q+Smite in jungle make you the farming boss. You can stay in jungle for days and invade the enemy jungle with ease and little chance of dying.
I'll explain more about the technicality of jungling/creeping with Nunu in the near future when I update this guide.

My base jungle route with Nunu is:
1. Get blue leashed and try your best to save your Q (kill it with smite)
Blue is necessary to jungle with Nunu, I strongly advise you kill it first!
2. You should get level two, take blood boil and head to wolves where you should boil yourself and kill the big wolf with your Q
3. Grab wraiths, by this time you should hit level 3 and be very healthy
4. Do golems as fast as possible, saving smite but Q'ing the big golem
5. Pick up red buff with BB+Consume+Smite
6. You should hit level 4, grab your E and head to the lane with the most likely successful gank. Boil your team mate and try to slow as many times as possible with your E. The maximum amount of Es your probably going to get off before they either reach tower or die is 3. This is if you're really lucky, so make sure your team mate/s have some CC also.
7. If you get a gank, either counter jungle or dragon with your team. If you miss the gank, do not be discouraged, counter jungle your enemy as much as possible while staying safe, then attempt to gank again. If you're too low, just go back and buy and return to jungle.

That's my jungle Nunu guide, though still partially incomplete I decided to publish it anyway, because I love you guys.
If you have any suggestions or comments, please tell me below, if you enjoyed the guide or found it helpful +1 it for a cookie, if you didn't like it or find it helpful then tell my why below and don't be afraid to downvote! I respond well to constructive criticism.
Anybody who wants to add me, as mentioned beforehand my summoner name on NA is: Ree Sing
I main jungle and have lots of fun playing with friendly people and it would be a pleasure to meet you.
I will update this guide often to finish it eventually,
Thanks,
Rev (Ree Sing).