You can either go, 3 AD damage Quints, or 3 Lifesteal ones. It's pretty much, "opinion based" on runes. But this Is the way I like it. Some sustain early damage, defense and some damage.

Farming with Zed, is really important. Since you're an assassin, you will be wanting to get fed, getting your items as fast as possible and just start oneshotting those carries on the enemy team!
So, basically. Each creep you score a lasthit on, you'll earn gold for it.
Zed's really good at splitpushing aswell, that's why I recommend buying the Ravenous Hydra
Because of the Passive Proc, and the ultimate waveclear it gives you.
Pre 9-10 around that time, you should just be having your PRIORITY at farming.
100 CS every 10 minutes, would be great, giving you the items you need fairly quickly.

+Pros
Very high damage, especially when ahead.
Very fun to play.
Very versatile.
Very good champion for carrying games.
Brings alot to the table.
Able to dodge skills with his Death Mark
One of the best splitpushers in the game.
Amazing Poke and Harrass.
Amazingly fun, and good jukes with Living Shadow


-CONS
He's very squishy.
He's a melee, short autoattack range.
Has no other escape except for Flash If Living ShadowIs on Cooldown.
He loses 1 hp, if there's any other ninja in the game.. For example Shen Akali Kennen :(((

Flash
This Spell, is basically the
main spell for everyone.
It makes Zed's kit very viable.
Since you're blowing your Death Mark
And most likely Living Shadow To get in range
You'll most likely need your Flash to get away.


Ignite
Ignite is very important for Zed
Not only the Damage it does to the person you put it on.
It also reduces the incomming heals on that person.
For an example, You use your Death Mark
And follow up with your spells, + Ignite.
Then there's a incomming Nidalee that wants to heal him up again.
Death Mark Explodes, and the heal wasn't enough.
Really important for Zed and his burst.

Runes, are very important for every champion in the game.
But you can also build champions differently, with runes like items.

Greater Quintessence of Life Steal I usually go with two of those.
Greater Quintessence of Attack Damage You can either go with three of those, or 1 and two lifesteal.
Greater Mark of Attack Damage 9 of those, or attack speed ones with the Attack/Crit build.
Also, Greater Mark of Armor Penetration Works just as fine!
Greater Seal of Armor Not as important in the midlane, depends who you're facing though. But it's a really good choice of runes, as there's not much else to pick for seals. x9
Greater Glyph of Scaling Magic Resist x9 Of those, or x6 and x3 Flat Magic resist.
In the midlane you're most likely going to face off against a Ability Power based Champion. Meaning, those will give you very good stats against their damage and burst.

Contempt for the Weak Zed's basic attacks against targets below 50% health deal 8% of the target's maximum health as bonus magic damage. This effect can only occur once every 10 seconds on the same target.

Contempt for the Weak And the Executioner mastery works really well together. Lasthitting works, perfectely aswell!

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Razor Shuriken Zed and his shadows throw their shurikens, each dealing 75/115/155/195/235 (+100% bonus AD) physical damage to the first enemy they pass through, and 45/69/93/117/141 (+60% bonus Attack Damage) physical damage to each additional enemy. Additional shurikens that hit the same enemy deal 50% less damage than the previous shuriken.

Razor Shuriken Is the thing we use to poke with, + our Living Shadow. It has quite a high energy cost at early ranks, so you will not be able to spam it nonstop. Living Shadow + Razor Shuriken Becomes a double Razor Shuriken Since, the Living Shadow Mimics the moves you make. You may also, reach much longer with the help of your Living Shadow's Q.
You wanna max Razor Shuriken 1st, then Shadow Slash > Death Mark into Living Shadow

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Living Shadow Passive: Grants 5/10/15/20/25% additional bonus Attack Damage.

Active: Zed's shadow dashes forward, remaining in place for 4 seconds. Reactivating Living Shadow will cause Zed to switch positions with this shadow. Zed's shadows mimic his abilities. If an ability strikes any target twice, Zed restores 20/25/30/35/40 energy. Energy can only be restored once per mimicked ability.

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Shadow Slash
Zed and his Shadow Slash, dealing 60/90/120/150/180 (+80% bonus AD) physical damage to nearby enemies. Each enemy champion hit by Zed's Shadow Slash reduces Living Shadow's cooldown by 2 seconds. Each enemy hit by a mimicked Shadow Slash will be slowed by 20/25/30/35/40% for 1.5 seconds.Enemies hit by both Shadow Slashes will be slowed by 30/37.5/45/52.5/60% but will not take additional damage.

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Death Mark : Active: Zed becomes untargetable and dashes to target enemy champion. Upon arrival, he marks the target for death and spawns a living shadow at his starting position. This shadow lasts 6 seconds and mimics Zed's abilities. Reactivating Death Mark will cause Zed to switch positions with this shadow.

After 3 seconds, the mark will detonate, dealing physical damage equal to 100% of Zed's attack damage plus 20 / 35 / 50% of damage dealt of all magic and physical damage dealt to the target by Zed and his shadows while the mark was active.

You can dodge abilities, such as Lux's Ultimate, Ahri's Charm. And basically anything, if the timing with your Death Mark is correct.

Focus on the highest priority on the enemy team, such as a fed Lucian or Ahri with your Death Mark.

Your Death Mark will spawn another Living Shadow Basically saying. If you use your Living Shadow behind your target, then you use Death Mark You will now have 2 Living Shadow's PLUS. You're own autoattacks and Razor Shuriken + Shadow Slash.

Use your Living Shadow Razor Shuriken Shadow Slash to farm out minion waves quickly.

If you're chasing an enemy, or being chased. Remember, either you can use your Living Shadow Forward. Or you could also Living Shadow into Shadow Slash To slow your enemy. And Razor Shuriken for more damage.
NOTE only your Living Shadow's Shadow Slash will slow the enemy, not your own.

Adding more info, later on. Have a time enjoying this one, for now! :) Thanks for reading folks!