Here is a guide of how I noticed Scarra built mid lane Zed. Instead of the typical, Maxing out Q. Scarra maxes out E then W. It's a trick he saw used in Korea I believe; moreover, the point of that is the bonus AD you gain from W (25% at level 5) is massive. Anywho, I'm here to teach you new Zed players to play like our Lord and Savior, Scarra.

The Fortitude Potion start, is a very good one for most AD mids. Especially the AD casters. I've even seen AP casters start it just for the free barrier of 120 health at level 1. Never forget to use it especially if you're ignited and flashed away, it'll instantly give you 120 health despite the ignite.

On your first back you should probably be able to insta buy a brutalizer. Possibly a few wards and potions as well just incase, due to not picking up any sustain at this point.

Second back you should buy a Bilgewater Cutlass, for that 15% spell vamp and active slow. That slow is very helpful for when you all in the other mid laner.

Third back finish up that Blade of the Ruined King, then look to finish your Black Cleaver, then probably buy some shoes at this point.

Then afterward it gets very straight forward, buy two Bloodthirsters for the sustain and also to build those stacks early, then build a Last Whisper because at this point they must of build some armor.

I cannot stress this enough, Zed is a very farm heavy champion. You will be utterly useless, unless you farm farm farm. Farm minions and farm champions. Zed is a very mobile champion, ganks to your top and bottom lane won't only give you much praise, but some free gold too.

Zed is a very easy champion to farm minions with, his passive makes it incredibly easy to do so. Around when the minions have a little less than 1 third health it's a for sure creep kill.

With this build all your harass shall be coming from the W-E-W combo. You will throw your shadow at the other mid laner, E to slow them down, then W to go to your shadow to land an auto. Very simple, very easy. However if you do not do it quick enough, the W may not be in range and you would have wasted time and literal energy.

Taking harass

Like I said before Zed is an incredibly mobile champion. Juking most kills and ganks is very easy with W. However in most situations mid, you'd like to be the b00ly. Harassing as much as possible to zone out the other mid laner. Preventing them from farming and gaining EXP.

Believe it or not Zed has a few combos.

The typical combo to harass would be
W-E-W
done in quick succession.

the Kill?
This is the normal combo to go in for the all in.
R-R-Cutlass/Ignite-E-AA-E-W-W-AA
You get my drift? However only press R a second time if they run towards the shadow, the shadow appears behind them however, so typically you'd want to go in head on. I typically like to ignite/cutlass early since our R will usually be the finishe, not the ignite.

Juke City?

Being ganked? Here's a little funny combo. Depending on the angle of the gank I'll assume you're pushed and he's coming from behind.
R-R-W-W
Boom you're a mile away.

Chasing someone?
W-W-Flash-R-R
It's pretty funny seeing how far you can move.

Another juke? Let's say you're stealing blue and they catch you.
R them, W-W over a wall, they run towards you, R back to your clone and run away.

There's quite a few funny combos you can do with Zed.

Typically as Zed you do not wanna go in first, you want the team to soften them up then come for the clean up. However you typically want to ult their ADC/APC. Near the center of the team fight. So your E will damage everyone around. Then use your W-W to chase the runners.

There's not much else to say, all comments and critiques will be appreciated.