Fiddlesticks is a very fragile champion and can die almost instantly, however this does not stop him from being one of the most game changing champions in the game.

One well placed fiddle ult can turn a loss into a win quickly. It is learning when and how to land these type of ults that will make you a good fiddle player.

Here are some high elo games played by me with fiddle.
http://clgaming.net/replay/2526/

http://clgaming.net/replay/2527/

I use a standard full ap rune page typical to most casters.

9/0/21 is also the typical caster build. Make sure to pick up 2 points in the increased buff duration.

I start with amp tome and 1 health potion.
I grab my Kage's pick and lvl 1 boots my first trip back to town.
If farming is going well I will straight rush an hourglass.
Then you can grab your death cap followed by banshee/abbysal
Finally I finish with hourglass and Rylai's which I feel are both luxury items and you will never get.

A lot of fiddle players will max fear first after 2 points in drain.

I think you only need lvl 1 fear for your first gank. Maxing drain allows you an easier dragon and overall higher damage if the lane you are ganking happens to have a cc as well.

Keep 1 point in E as it is a one point wonder.

I use flash+smite which is standard on almost all junglers.
Flash is great for jumping over walls and closing ground with your ultimate if it wiffs.

The route I like to take I start at wraith camp. I smite big wraith and drain one wraith to death. Then I auto attack down one of the wraiths down and life drain to finish the last small wraith.

After that I walk to Wolf camp auto attack to pull the big wolf and then drain that down. Take your health potion now while walking to blue. Auto attack pull the golem and drain it down using smite when it gets into the 470 health range. Drain the rest of the camps down and clean up the 2 small wolves you left.

Clear red, small golems and the respawned wraith camp then port home to buy your kage's pick and lvl 1 boots. Then you can gank or continue farming.

http://www.youtube.com/watch?v=U4M_Y26aUL8 This is another route you can take as well.

Fiddle can be a great initiator in some cases, however the majority of the time you want to ult in with fiddle once the fight has already broken out and the cc has been thrown. This way you can be sure to be able to use all of your abilities and land a full ult.

When you ult hit the main target you want to hit with your fear instantly and follow up with a dark wind + life drain.

One of my favorite ways to gank with fiddlesticks is have the lane you are ganking push the lane all the way up to the tower.

Work your way into the brush and wait there for the lane to push back up. Ult from the brush and collect free kill.