Fiddle is a sustain jungle that is very reliant on his abilities. When played right he would never really have to auto attack another champion and instead would do most of his damage through his ultimate and drain ability. A lot of lower players only cares only for his ultimate but his other abilities are actually quite deadly. His drain is surprising deadly. During early game he can 1v1 most champs if his drain is not interrupted. When timed right, he can even kill people foolish enough to duke it out with him with a last minute crow(try to land it with creeps nearby). His fear is one of the best disables in the game lasting an eternity. Lets not forget his ult. When landed right it would absolutely destroy the other team and would guarantee victory in almost every team fight.

Pros

High sustain in jungle
Great Team Fighter
Great assassin against squishies
Drain and fear combo is amazing even though require no skill to use
Great 1v1 when played right
Amazing disable
Baron/Dragon wall ult smite steal is amazing

Cons

Clears jungle rather slow
Squishy
Clears lanes slowly
Feels too easy to play
Weak auto attack
Can't 1v1 well when ignited

Fiddle is a lot like Warwick in his jungle banks. Without lvls his ganks are rather weak. The best time for fiddle to start ganking is at lvl 4 where he will have a good contribution of damage and a 1 sec disable if you follow my skill table. This may be the best time to gank but kills at this lvl is still hard to get. This added to fiddle's clearing speed, it may be best just to wait until 6 before ganking. At 6 most of his ganks should equal a kill.

Fiddle jungle should start at blue since his early mana thirst is great and the cd he gets will help him clear faster. He is capable of soloing blue without pots or smite. Kill golem with drain then auto 1 lizard until drain comes up. Then drain the full hp lizard and finish other lizard with auto. Then move to wolves. throw crows at blue wolf and drain big one. Kill all blue wolves and by that time drain should be back up and so finish big one off with drain. Crow the small wraiths. Drain the big one. Kill small ones and drain big one again. Drain big lizard once then smite and throw crow at it. kill smalls ones with drain. For the 2 golems, drain the big one once then throw a crow at the small one. That should kill initial 2 spawns of the small golem. auto or drain the big one to death. Then find a lane to gank or go back to wolves right now. They should spawn about the time you get there.

His basic combos is pretty simple. Fear and then drain immediately followed my a crow at the end.
To land the perfect ultimate is the only hard part. Fiddle needs to be surprising, ulting into the back line with the squishes is the key to victory. When ulting try to make sure you are not noticed, usually jumping over walls and hiding in bushes is best. Know all the areas you can jump over and prepare to flash if you miss by a few inches. Watch out for Lee kicks and vayne pushes cause those can screw you up. Either fear those guys or hit zhonya before this happens. When your ult lands try to fear the add or their most vital not too tanky guy. Then don't be afraid to throw the crows and drain a little before Using zhonyas. Only activate Zhonyas if they are going to stun or burst you down. A stun can quickly end you as you are easily burst down. Make sure to focus 1 person and make sure that person is dead before switching main target. If you get greedy and try for 2 there is a chance that both will survive. If you follow these rules then you should be able to carry most games.