This build currently one of the best ones you can get for fiddlesticks. It provides a great ammount of spell vamp, Defence and Damage. It allows you to deal great ammounts of damage while staying alive even if focused. Remember this thought, Zhonyan's is good for when you're about to die but it's also good for when you have your ultimate open and you're being focused. You can use it right there and keep dealing damage with your ultimate, then flash right out of the fight and come right back and continue dealing damage also this is a little risky to do if they have champions that can jump you right back when you flash. You must be sure they won't get to you.
Your rotation with Fiddlesticks is pretty simple but also tricky.
For example when youre fighting against teams that can interupt your Life Drain then you must be sure that they will do their stun/fear or whatever they have and then you can cast Silence and Fear and then continue draining them till they are dead. For example if a team has Xin Zhao and you're being focused by him wait till he knocks you in the air and then use your spells.
In Duels, your rotation is simple, you open with silence then fear them and drain while they are in fear, then if you're not sure that you will survive for 3 seconds till your fear and drain are out of cooldown then kite them till they are elsewise just continue draining them since Drain is out of CD right when you finish casting it, but this is risky because if they can interupt it or outdamage it because they are fed you will die for sure.
And one last thing for your rotation, when youre chasing them never stop to silence except if they are extremely low on health or you are sure you wont reach them after a point. If you can actually reach them then dont silence, keep running then fear and drain then use silence cause if you use it before the drain it will interupt the fear.
In the Jungle
In the jungle you're going for Wolves > Blue > Wraiths > Red > Gank 1-2 lanes (one that really needs help and the other for the free kills) > Recall > Wolves > Golems > Wraiths > Steal their blue ( but be careful ) > Gank. Then teamfights should be started (Level 11-13) if not go farm a little and then go for your blue.
An other thing that is a must is that your teammates should NOT be pushing their lane. Fiddles can't dive, he will simply not catch them so the lanes need to be pushed for your benefit and also tell your support to get vision wards the first time they go back.