Focus :
To play Spiddle you must be willing to be patient and work together with your ADC. As a Fiddle support it is very easy to stack up on kills as the game goes on, especially once you understand him better. But you are still a support, you're there to aid the ADC. If you're doing well, great, but don't start stealing his minion feed, being disrespectful to him/her, or any other manner of negative behavior.

In this guide I play Fiddle as a "tankier" character. If you don't and start to build pure AP he gets killed way too easily to be of any threat, especially if your team doesn't have a lot of peel. He focuses on hp and AP to survive in team fights and win solo engages by just standing there and healing.

I usually go with flash because he has low mobility and heal for my ADC. The heal adds movement for both of us (Which Fiddle needs) and can help when you are caught off guard and stunned (or the like) when casting Drain.

Pros :
Massive life gain
Crowd control
Steady consistent damage
Can win in surprisingly tough situations
His passive is stacks with Abyssal Scepter

Cons :
Squishy early game
Low mobility
Dependent on a decent ADC early game
Dies easily if drain is interrupted too often
Ultimate is on a long CD

How to level up :
You need to focus on leveling up your Drain ability as quickly as you can while still getting one point in Dark Wind and Fear. Drain will heal you for a surprising amount, you'd be amazed how much damage you can take with that ability. After maxing Drain focus on leveling Dark Wind and Fear equally so as to maximize your crowd control.

How to use Fear :
Fear should be used when your ADC is in position, punish the enemies for walking too far out into the lane. Sticking to the bushes is a good way to keep your opponents at bay as they don't want to risk getting Feared and Silenced. Also make sure to take great advantage of when a support and ADC split up as the support goes to ward a bush or various other reasons, punish them for their mistakes.

How to use Drain :
Don't get cocky once you understand the full power of Drain. It can out heal most damage early/mid/late game surprisingly and the "tankier" you are the better chances are you'll make it out of the exchange alive. Just watch out for stuns and and incapacitating abilities. If you fail to watch out you will mostly likely be burst down before drain resets. This ability will be your bread and butter in any engage.

How to use Dark Wind :
It costs a lot of mana early game if you use it too much. This is why you need to watch for when there are few minions left in lane. At this point (Assuming 2-3 minions are left at low health) you can toss Dark Wind out and it can distance the gap between the enemy minion and the enemy champion. Then hopefully it will bounce between the enemy support and ADC.

How to use your ultimate :
Fiddle's ultimate is easy to see from a mile away. You are better off running into a bush and ulting out of the bush. It is a great idea (If you are aware of your strengths and weaknesses , would only recommend once you understand Fiddle better) to bait some enemies into a bush and ult out, followed with a Dark wind to silence them all and a fear on a target. It is easier to cast your ult into the middle of a team fight and using flash alongside your ult can really help you gain some kills. Be careful with using Zhyonia's right after you ult in, those few seconds of motionless invulnerability can cost you a kill or two.

I rush Ryali's crystal scepter , picking up Amplifying tome first. I then (Depending on how well we are doing) tend to get Giant's belt as my next item and then buy the full scepter. After that I tend to get abyssal scepter to maximize my damage out put from my ultimate and Drain as they are both need to be close to the enemy. Afterwards I get Zhyonia's or Banshee Veil , either one gives you a nice ability for Fiddle. It's up to you at this point what you feel would be best for you.

Zhyonia's and Rabadon give you a lot of ability power to really mess things up along with Zhyonia's activated ability which can be used with Fiddle's ult.

Banshee's Veil and Guardian Angel give you a great deal of survivability which is very much needed with Fiddle's naturally squishy nature.

Archangel's staff also adds a lot of survivability and damage as it increases your mana pool and gives you more AP at the same time. I wouldn't recommend this before the second or third item as it takes away from your "tankier" build.

Feel free to buy a mana potion or two at each visit as it drastically increases your chances of survival as Fiddle is mana heavy early game.

I go with an all ability power rune set because the Drain will heal you for any damage you take from lacking MR or Armor, which you should get through items in game anyways. I've never had a huge issue with this rune set.