Hi fellow LoL players,
I'm NickTheGreater - I am a Zed Main since Season 4 currently 150K mastery with him.
Platinum level Zed player currently bouncing between ranked teams. Recently got a new computer, so I'm aiming for Diamond this season!

This guide will teach you everything, I mean everything, about playing Zed to his full potential. Zed requires TONS of practice to pull off, but is highly rewarding and in my opinion the most fun champion out there. Nothing feels better than pulling off that game changing outplay blowing a team's engaging CC while killing the ADC and still getting out alive. So satisfying.

I always go Armor Pen marks, because dealing true damage to your lane opponent is fun. Full AD runes are also fine (15 AD, 9 Armor, 12 MR) but if you can afford them, get armor pen. I am not a fan of using Cool down reduction glyphs, you absolutely need the Magic Resist. Yes, CDR runes get your ult up faster in the mid game, but that's all you will use them for. With 0% CDR on Zed you don't have enough energy to spam Q to make the CDR worth using.

Zed is all about snowballing your lane advantage, which means winning those early all-ins with your lane opponent. Even if you're against an AD mid, their jungler is most likely going to pick AP to compensate in which case MR is still superior.

Thunderlord's Decree 99% of the time. Storm Raider's Surge is another option people use, but if you're playing Zed correctly there won't be a target alive to chase down. The only reason to take Storm Raider's is to chase down that Blue build Ezreal with QSS or to better clean up team fights. Attempt at your will, but Thunderlord's is best IMO.

You will pretty much never start anything but long sword and 3 pots. With my rune page, 10 extra AD from the starting Item is strongest.

On first back you have MANY options.
This is the most crucial item decision you make ever in League of Legends. I'll break it down for you.
Against AP Mid (losing) - Hexdrinker
AP Mid (Winning) - Serrated Dirk or B.F. sword
It is always except-able to have 5 Long Swords on your first back, they all build into something.
AD Mid (losing) - Phage + Doran Blade
AD Mid (Winning) - Rush Duskblade or Ghostblade

Personally, since I have been playing Zed for so long I usually rush a Bilgewater Cutlass.
This item gives you sustain to survive the all too real mid lane poke, in addition, gives you an activatable slow/nuke. I use this item for its utility mainly. The slow increases your change of the double shuriken combo of hitting, and gives you more burst while your ult is ticking. However, if you struggle with remembering to use the active, then you can just get a vamp scepter for the sustain you need.

Zed is a very weak champion until level 3. Level 3 you get access to your W+E+Q combo which can proc Thunderlord's. About 90% of the time as Zed you are against a ranged champion. Use your Q to harass if they step away from behind their minion line; hitting them now does the full damage of Q. Most of the time, they will be behind their minion line. In this case use your Q to farm and try to line up getting the last hit with your opponent. Your Q will last hit the minion and harass your opponent at the same time. Use your Q on cooldown until level 3. At this time try to save it until W is back up.

If you are getting a lot of attention mid, only use your W for harass about once a MINUTE. If the the enemy jungler sees you holding on to your W and just using your Q to get farm they most likely will no gank you because you will just W away and waste their time. If you see the enemy jungler show cross-map, now is your chance to throw out your W+E+Q combo.

Zed requires immense knowledge and map awareness to win the game. After you snowball lane, it is extremely easy to throw the game by attempting to overextend and get too greedy. Try to play even safer if you are the fed one on the team. At this point, you want to avoid dying so you don't give the enemy team bounty gold and experience. Also, you will want to maintain your EXPERIENCE lead over the enemy team. If you snowball correctly, you can be level 12 when the enemy ADC is level 9. This difference alone will rape whoever you target.

Zed sucks in team fights unless you have Quick Silver Sash/Mercurial Scimitar. The best play you can make in a team fight is to eliminate 1 person and soak important CC. OR you can wait for your team to engage and watch the fight play out while waiting to clean up once they are all at 50% health. Zed's passive allows for Amazing clean-up potential.

The classic complaint with Ranked Games- "I won lane but the rest of my team was feeders"
BOO HOO. As Zed that doesn't matter (Actually as most champions it doesn't but zed especially). Whenever you win lane, but your team is feeding - Split Push.

Split Pushing will win you the game about 70% in my experience. All you do is set up in a side lane (my preference is Top Lane when on blue side, and Bot Lane when on Red Side) and push Tier 1, Tier 2, Inhibitor Tower etc. The enemy team will most likely send only one person to stop you in which case KILL them immediately. Tower dive if you have to. Just kill them. Sometimes the entire enemy team will collapse on you and try to stop you. You should have a trinket ward in their jungle to see the threat incoming, but you should be watching where they are grouped at to see them leave and get you. If the enemy team is missing, you should be gone already. If somehow you get collapsed on, well take as many down with you as possible. Many times you can go super aggressive, get a kill, then ult out to safety. Also, if you take long enough to go down your team of feeders might get a mid tower or baron. Win-Win.

Pros:
Strong laner / 1v1 Champion
Long Range Combo
Mobile
Strong outplay potential
Fun to play and looks like a bad ***
3rd best Split Pusher in the game (Fiora>Jax>Zed)

Cons:
Zhonyas is OP
QSS removes his ult
His combo leaves him vulnerable with no escape
Terrible vs hard CC and tanks

Freezing mid lane wave is a good strategy to not only get ahead but also to keep your opponent down. If you freeze the wave on your side of the map you can start using your Living Shadow (W) for your combo without putting yourself at risk for a gank. Also, freezing lets you stay in lane for a long time so you build up a huge XP advantage over the enemy team.

As mentioned a bit in the Ranked section, Zed is unstoppable with proper team communication. If you can get a good split push going on Zed, then you will either get a kill and a tower, or your team will get a tower across the map or even Baron Nashor. If you can communicate with your team to make sure they disengage any 4v5 they encounter while you are pushing, then you gain a huge advantage for your team.

When split pushing, I try not to use my W to clear the waves just in case I am ambushed.

Against a stronger melee champion, a good strategy would be to ult then reactivate to maintain distance from your target while still being able to land Q and E on them for ult damage. If that combo takes them low enough then you can use your W to re-enter melee range for the execute. This is usefull as most split push match-ups will have you up against another melee champion. Using this technique will also outplay any Zed mirror-match you face.

If your Thunderlord's is on cooldown but your combo is back up, sometimes its better to wait for Thunderlord's to come back up before going for more harass. Also, try changing up the timing of when you throw out your Q after you toss out the shadow to make the timing unpredictable for you lane opponent. A lot of times you can predict them side stepping after you shadow because they are expecting to dodge your shurikens. Punish it.