Fiddlesticks Runes explained
There's one set of runes for Fiddlesticks on patch
11.15
that is the clear favorite for LoL players and pros alike. The best Fiddlesticks Runes on the position 
Jungle are Domination as the primary path and
Inspiration as the secondary path with a pick rate of 97%. Besides runes you should take a look on Fiddlesticks Build and if you are interested in pro matches take a look at Fiddlesticks Probuilds. If you want to discuss
Fiddlesticks then you should visit the champion subreddit.
Primary path on Fiddlesticks
Domination improves burst damage and assassination tools on Fiddlesticks. Most of high elo players – and our LoL pros in the the major regions – have agreed that
Predator is the best keystone rune to run on
Fiddlesticks. As soon as you buy
Predator. After a short cast time Fiddlesticks gains bonus movement speed, while moving toward enemy champions. This keystone rune is perfect for roaming and ganking. This is usually followed up by taking
Cheap Shot,
Eyeball Collection and
Ultimate Hunter.
Cheap Shot makes you deal more damage to enemies with impaired movement, which has great synergy with the setup of Fiddlesticks.
Eyeball Collection is next up. This grants the user additional damage with every killing they score.
Ultimate Hunter scales up Fiddlesticks ultimate haste on every unique champion takedown.
Secondary path on Fiddlesticks
When it comes to your secondary path, most
Fiddlesticks players prefer to go with
Inspiration.
Inspiration opens creative opportunities on Fiddlesticks troughout the match. On the
Inspiration path, the best runes for Fiddlesticks are
Cosmic Insight and
Future's Market.
Cosmic Insight grants summoner spell and item haste. You can enter debt to buy items, which is displayed as negative gold in your inventary. A small lending fee is added onto the amount of gold you owe after leaving the shop.