Hi All
Here's another Nunu & Willump support guide for you. I have been playing Nunu for quite some time, but began life out in the jungle. It's useful for you to know that I'm not a pro player, I'm simply 1200 elo in soloque.
The purpose of every guide should be to get the reader thinking – this guide will not tell you what you MUST buy and what spells you MUST level, but just give you the thought process behind each of the choices you have available. Please remember, make your character work for you. I personally like high mobility, and so my build reflects that (masteries / items etc), you may not feel that it’s important, so build your Nunu slightly different.

Pros / Cons
That's it!

(Passive) This passive seems pretty useless, and although they have improved it from 7 down to 5 basic attacks, it’s still not what you’d call powerful! However, I would highly recommend auto-attacking minions in your lane when you get the opportunity. It will help you stay in lane. This coupled with Consume means that both your mana and HP levels are within your control – use them wisely.

(Q) This is really useful to help keep you in lane, but does scale poorly as the game goes on. Since you level this last, at level 14+, it doesn’t heal for a significant amount, as you will be running around with at least 2000hp. Although in theory levelling this up sounds like a good idea, it is no where near as powerful as your W or E.
Bloodboil
(W) This is your bread and butter as a support. It's cheap to cast, and beefs up your AD Carry all day long - you can literallly have this active the whole time! But use it when you want to push, because you do need to look after mana a little bit.

(E) - Often referred to as Snowball, this is what has defined Nunu in the past. This ability is still useful as a support, as it actually reduces the damage the opposite AD Carry can do (by slowing their Attack Speed). It also helps with harrassing. Early game, this is worth casting as the damage will help out. However, later on it becomes purely a utility spell, that doesn't really scratch the enemy, but really does annoy them!

(Ultimate) - this is your power-house move. It does big damage in a big area, and also slows movement and attack speeds whilst channeling. If you were building AP, I'd be screaming to get a [Banshee's Vial] so it's harder to interupt. However, the damage you deal generally will mean that you are much less likely to be focused whilst playing a support role. Therefore, their CC and interuptions are going to be aimed at your AD/AP Carries. This move should be easier to pull off as a result.

These are my preference, and why:
- 1 extra pot isn't really worthwhile!
- I personally enjoy a mobile character, and with the oracles you will buy in the mid game, it really helps you make the most of it
- I actually quite like this, though it's not everyone's preference.
- the only buff you'll ever get is Nashor, and although useful to have it for longer, you are not the 1 who is going to carry your team when you do get it. So, just hurry your team along when the buff turns up! I do consider this surplus to requirements.
- I had a spare point and don't see it going elsewhere. The masteries are much more important early game, and this does help you stay in lane whilst you need to.
- your ulti has a horrid cooldown, as does your consume. Consume helps you in lane, and i dont need to talk about the ulti!

Now that you understand the abilities that are available, you should be able to make informed decisions on how to set up your skill sequence. But for some further guidance, here's what to consider in the very early levels:

Not long on here people!
is a must, best escape spell in the game, and Nunu is no exception.

Viable Choices

In premade games, I'd recommend Clairvoyance as you should have the communication in your team to be able to gain some good map control. It's much harder when you are typing "please use CV here"!
Heal can be taken if your AD wants to take ignite or exhaust. If they take heal, you take exhaust. Simplesssss

I would not consider any other summoner spells

Team setups that favour Nunu & Willump require AoE damage. Amumu and Galio have a nice stun that allow you to use your ultimate without it getting interrupted.
If your team are playing with an AP Jungler, plus AP top, you are limiting the number of great options for your bloodboil (once team fights break out). As a result, I would recommend encouraging AD chars rather than AP. The more AoE the better!

Rather than re-writing what someone has already done, please see the guide below for more information:
Warding
Many people will place wards in a similar place to this - if you are using an oracle or vision wards, go check these places to be able to destroy enemy wards!

Thanks for reading this far. I will continue to make improvements, and feel free to comment. Key for any support is to ward the map effectively, and stop the enemy from warding at the same time - anyone can cast the spells in a specific order, or buy items that some guide tells them is right, but supporting your team in the best way takes practice. You need to understand who to aid most in your team, and who to shut down in theirs.

Happy gaming