Levels 1-2
This is the weakest point in your laning phase, and the stage of the game where you can’t really fight back. You can throw a few Q’s, you can kill a few minions, but you’re generally helpless against ranged champions—which are the main adversaries you will be facing in the mid lane. In melee lanes, however, you’re actually pretty strong at doing quick trades. Don’t go further than that, though, any extended trades will most likely be lost, since you run out of steam very quickly after using your abilities (figures, you’re an assassin). You mainly want to farm here, throwing Q’s to either last-hit or poke your laner.

If you’re against an early game jungler, like Lee Sin, Elise, Shaco, warding the side they started on is highly recommended. Most of them start Brambleback (Red buff), which makes it a lot easier to predict their pathing. Adding to this, play to the side opposite of what they started. If they started Red, keep to the side your Red is at. This makes it a lot more difficult to gank you, because the distance between you and them is almost double of what it normally is-—if you were in the middle of the lane.

If you aren’t against one of those enemy jungler , you can usually expect them to gank from the side opposite of what they started at, at approximately 3 minutes, level 3. Therefore, keep to the other side at around that time, and if possible, ward the side you’re occupying because they could always pull a fast one on you.

There are 3 main ways laning phase is usually played with Zed. One is letting the waves push towards you, freezing and zoning your opponent. The second is hyper-aggression, pushing the waves and trying to whittle your opponent down constantly with Qs and then going for a kill level 2 or 3. The third is pushing the waves to ignore lane and permanently roam.

The first way is what I recommend for people learning Zed, as it’s the one with the least amount of risks. It’s low risk, high reward, which is wonderful. The second, the one focusing on extreme aggression is a playstyle I would only recommend for people who are quite experienced with Zed, and knows their damage. It is high risk, very high reward, and it can absolutely be preferable to the first playstyle if played correctly. But, if it fails, you’ll essentially be half a champion for the rest of the game. The third strategy is only really used against champions you won’t be able to kill at all. Someone like Galio or juggernauts prompt this playstyle, so be ready for it.

Levels 3-5
Your power is ramping up, and soon, you’ll reach your final form. You’re pretty strong here too, all things considered, especially at level 5, where your shurikens deal significant damage. This is also where you’ll pick up most early kills, with a cheeky W-E-Q into them dying from either an Ignite or your basic attack. To actually hit this W-E-Q, you can rely on abusing their AA’s, since every champion in the game needs to CS. Whenever somebody is about to last-hit a minion, they’re stuck in that animation, leaving them open to attacks. Use this, and I promise, they will die. Eventually, they will all die. You’re also very likely to be ganked within this timeframe, so while you do have strong kill potential, you need to be very careful about when and how you use your W.

Levels 6-13
Your biggest surge of power, these levels are your most important out of all. This is where Zed shines, and with that, where you need to shine. Because you’re hitting many very important powerspikes (namely level 6, 9, 11 and 13) within these levels, you need to use your time wisely. This is where most of your roams will happen, this is where most… everything, will happen. You can invade, you can duel, you can straight up one-shot, if you’re given the option, and there’s nobody to stop you.

Now, let’s talk about the specific levels in detail, beginning with, well, your 6th level, which grants you access to Death Mark. This is your biggest powerspike, in terms of kill potential. Because of this huge increase in both mobility and damage, you’re often going to find yourself much, much stronger than your lane opponent. Therefore, unless they’re in a position of power themselves (like, in a very difficult matchup/lane), you’d be favoured to look for an all-in at about this time—preferably before they hit 6 themselves. At least, if anything, start setting up for an all-in after you’ve hit this powerspike, because you’re also very strong in the coming levels. It’s worth mentioning that there are many a champion you can Flash + R onto the very moment you get level 6, and these champions are ones that do NOT have any very punishing CC they can hit you with the moment you appear from your R. So, not champions like Ahri, Lux or Morgana (unless they used their CC just before, in which case, go ahead), but champions like Viktor, Karthus and pre-level 6 Cassiopeia are perfect targets. If they Flash away, you will just follow them with your W combo, and if you hit everything, it is very likely that they will die (especially with Ignite).

Speaking of, let’s move onto the time where you hit level 9, which is the time your Q’s will have maxed out their base damage. This is a pretty considerable boost to your overall damage, so while it doesn’t compare to the colossal rise in strength level 6 gives you, it’s still a notable and important power surge to bring up. Just like before, an all-in here is a very possible and favourable action, since most mages still haven’t scaled up to their peak potential.

At level 11, you gain a relatively small, but noteworthy enhancement to your assassination potential, as you get to upgrade your Death Mark to rank 2. It ups the percentage of your damage that’s stored in Death Mark from 25% to 40%, so while it doesn’t actually increase the base damage of your ultimate, it basically does, since the percentage damage is like… 95% of the damage.

Finally, at level 13, both your Q and E are at their full potential, granting you the highest base damage they have to offer. Your assassination potential here is essentially at its peak, but because you won’t get any more base damage from levels anymore, you’ll slowly dwindle down to a more balanced level after level 13.

If you’re roaming, remember to keep an eye on your jungler. Roaming or invading with the jungler is a lot better than roaming alone, for obvious reasons. Though obvious, I’ll state those reasons anyway—you get more power in general, by virtue of a likely numbers advantage over your opponents, and if you do succeed with the gank or invade, it’s much easier to transition that into an objective, seeing that your smite-bot is there with you. At worst, it becomes even in numbers, and if so, Zed is great at assassinating any of them, removing them from the fight, giving your team the numbers advantage again.

You thought that last part was about late game? Yeah, no, that was about late laning phase. Let’s actually talk about your late game, which means, levels 14-18. This is, aside from your lackluster early game (level 1-2), your weakest point. It doesn’t mean that you’re weak, just that it has reached the point where the game probably should’ve ended already. Your enemies are scaling up, they’re getting items, and most carries will likely have either a Zhonya's Hourglass or a Guardian Angel. Adding onto this, this is where your targets (ADC’s and mages, for the most part) are at their peak in power. They’ll destroy your entire team if you don’t do anything about it. This is where Zed, not as a champion, but as a champion class, falls short. Zed is actually very strong in the late game compared to many other assassins, but assassins in general are not supposed to be strong in the late game (in teamfights), because of their usual early/mid game dominance. So, while Zed is a good late game assassin compared to the standards, he is still a champion with (almost) only purely burst damage and mobility. This can make it difficult to compete with the late game prowess of marksmen, mages and melee hypercarries. Of course, you will still deal ludicrous amounts of damage, but it’s more difficult to actually use it here, since aforementioned champion classes will have built defensive items to royally ruin your day. Adding to that, your targets will most likely be surrounded by multiple other champions, like the support and jungler, making it a troubling matter to reach the prey you’re hunting.

So, how do you go about it? Well, you’ve got a few options, all of them useful for different situations.

You can splitpush, drawing the enemy team’s attention towards you, making it a whole lot easier for your team to take objectives uncontested. If you execute the splitpush correctly, you can force the enemy into making a decision that has no clear answer. They either send somebody to deal with you, leaving your team in a 4v4, or they try to brute force a 4v5, leaving you alone to push down their towers. There are a few requirements you need to check off before you start splitpushing, however. The biggest downside to splitpushing as Zed is that you’re unlikely to have teleport, which makes splitpushing a lot riskier and strictly worse. So, a lot of the time, the reason a Zed wants to be on the sidelanes is to gain XP and gold as quickly as possible, to prepare for the inevitable teamfights.