1. Go Duskblade of Draktharr as a general item, and when you need extra Ability Haste. The item gives the same stats as Prowler's Claw but different Mythic Passive. Ability Haste is very important for Zed.

2. Go Prowler's Claw when you're against squishy champions who aren't building a lot of armor. Better for 1v1.

3. Go Eclipse when you are going against tanky team comps. When going Eclipse, your secondary runes will be Sorcery and most of your items will be Ability Haste items.

1. You'll buy Serpent's Fang when the enemy team has a lot of shields.

2. Buy Umbral Glaive when you are planning to gank a lot to clear wards.

3. Guardian Angel against enemy teams with a lot of AD or Kill Pressure.

4. Buy Maw of Malmortius against Heavy AP.

5. You'll usually go Infinity Edge as a super late game item. Sell your boots and buy an IE.

Go for the Electrocute rune page when against squishy champions. Go Taste of Blood as default or against poke champions. Go Sudden Impact against squishy melee. Always go Eyeball Collection. Ultimate Hunter as default. Relentless Hunter if you are planning to gank a lot. And Treasure Hunter if you know you can snowball.

Run Conqueror when against a lot of melee or tanky champions. Always go Presence of Mind since you're an energy champion. Go Legend: Tenacity against CC or Legend: Bloodline against melee and tanky champions. Since you're an Assassin, you'll always go Coup de Grace, unless you are going against all Tanky champions, then you'll run Cut Down.

Secondary Runes:
Your secondary rune page will be Sorcery. You will always take Transcendence because of how valuable Ability Haste is. Next is either Scorch as default. Nullifying Orb against heavy AP or Gathering Storm for late game scaling.

Q&A:
So what about Precision and Domination for secondary? These rune page is still good as a secondary but again. Sorcery just outshines them both. You can go Presence of Mind and Coup de Grace with Electrocute if you have trouble with hitting your abilities. I would recommend to never go Domination with Conqueror because you will need the Ability Haste.