A Few Tips for Fiddlesticks Support

Against him that is!

1. Mind his level 6, Fid's ult does a ton of damage and being a Support does not tone it down all that much. Ping MIA when he's not on-screen as that means he could be roaming to other lanes. Supports can roam. Honestly you should do this anyways since he can Flash+Q and lock-down anyone.
2. Watch the walls, Fid can ult over those. This may sound like common sense but I had a match recently as Fid Support (which I was doing before it was cool!) where the enemy bot-lane continued to push up to our turret, not ward over the wall, and promptly die when I Fid ulted over it and behind them. I straight-up counted in chat how many times they did it because they clearly weren't learning. Ward. I mean it- he gets to hop exactly one wall. If you don't have vision of him and it's post-6, operate like he could be anywhere and act accordingly. Fiddlesticks relies on his opponents putting themselves into bad positions to do well- don't give him the advantage.
3. Separate when needed, cluster when needed. You would much, MUCH rather be near a creep wave than alone only with your lane partner. The former means you'll only be hit once by his Crow as it has no priority except to find something it hasn't hit yet, the latter means it's going to bounce back and forth to get more damage off on you. This becomes especially important if Fid commits and uses his Drain on you- that is the only way his Crows have priority. They will bounce back to his Drained target every chance they get. If Fid keeps Crowing the wave then it's going to push- get a Jungler on-hand to take advantage of this.
4. Mind the Drain. While most Fid supports I imagine max Fear or Crow for CC and harass respectively, the Drain is not something to take lightly. At level 1 with no AP it does 400 damage and heals him for 60% of it if fully channeled- don't ignore him just because he's a support. If you get a chance to get out of range and still fight- take it. Packing ignite is only so helpful since even if you reduce the healing- it still does a lot of damage if you leave him unattended.