Invade Fiddle in the early game to deny him as much gold as you can. He is weak before level 6 but even weaker before level 3 so use that to your advantage.
When Fiddlesticks reaches level 6 he will try to surprise gank you with his R. Keep track of where Fiddlesticks is and inform your team, so they can get wards down and play safe when he is on their side of the map.
Before engaging on to Fiddlesticks, ask yourself if this is the real one. Don’t waste everything on a fake scarecrow.
When sieging an objective, make sure you ward around the objective in question to catch out Fiddlesticks before he engages with his R. Deny his surprise engages by warding around your team.
Seek fights when Fiddlestick’s R is on cooldown because with it down his team fighting potential decreases a lot.
Do not group to closely together when dancing with the enemy. As Fiddlesticks R can deal tons of damage to your whole team if you're grouped close to one another.
When Fiddlesticks gets access to 3 abilities, he is really difficult to deal with because they offer him so much utility. If you’re trying to go for an all in, make sure to fight when 1 ability is missing.
Once Fiddlesticks has his Zhonya’s Hourglass, it allows his Ultimate R to really hit home. If he channels his R and uses his Zhonya’s, you can’t attack him when he goes into stasis.
At level 6, Fiddlesticks ganks will become stronger and he will look to constantly gank when he has his Ultimate R up. Prepare for this and try to delay his power spike for as long as possible through invading.