In Laning Phase, Katarina is pretty weak. However, there are a few things you can do.
Level 1: Just focus on last hitting with Q's. Don't walk up and don't take any poke,just stay healthy.
Level 2: Grab E. If you are taking electrocute, you can trade with Q, E, auto. If you are taking conqueror, I recommend waiting to trade until level 3.
Level 3: This is a strong powerspike for Katarina. I recommend trying to trade in most matchups at level 3. The current best trading pattern (with conqueror) is with E, auto, W, auto, Q, auto, E, auto, and finish them off with ignite. Make sure you use your w movement speed to dodge any skill shot cc thrown at you. In matchups such as lissandra where they have a non skillshot cc with a range to it, try to trade with q and e, and when you e onto your dagger stand at the max range and w away from them so that they can't root you. Generally these abilities having longer cooldowns, so you can trade them again before their abilities come back up.
Level 4-5: At this point how you play the lane depends on the earlier levels and there are many things you must think about.
Things such as: Do I have a kill yet? Can I kill my laner? Should I play safe? Can I roam? Where is the enemy jungler? These things will help you determine what you want to do next.
Past level 6: If you gain a large lead (2+ kills) before level 6, then past level 6, play very aggressively as long as the enemy jungler isn't very fed. If the enemy jungler is behind or even with your jungler, then a skilled Katarina is able to 1 v 2. If you aren't confident on her, then don't try this. Just focus on roams and plays on the map. Swap to sweeper and pick up control wards to help your roams. Try to always be available to make plays on the map.
Mid Game: This is where Katarina really shines. Her 3 item powerspike on both AD and AP is very great, and she is able to consistently hard carry her team in teamfights if you play it correctly. Look for picks on overextending squishies. Try to position yourself on the flank of the enemy team so that when they engage you have free access to their backline.
Late Game: Katarina is still pretty strong late game. There are many ways to play her at this point but currently, the playstyle of waiting patiently for enemies to waste key cc abilities with long cooldowns and then jumping in to kill them and jumping out is the best strategy.

---

This chaamp is not a Killer. She can be Wing or can be Iron.
Is up to you choose what u want to build and what u want to do with this champ.
This Champ is:

Assassin: well....you already know this....
Tank: Katarina can be a real tank with real tank stats and still kill a lot.
Split pusher: Lot of Item grant you a lot of split pushing Potential.
Bruiser: Why trust a 0/5 Kayn when you can do the first move and hope to your iron 5 teammates to join the fight?

---

---

I will be more than honest. COnqueror and Dark Harvest are the best rune for Katarina on every matchup and on every item path.
Later you will ask yourself about some other rune mechanics.

I will answer to you: Basically almost every rune run well and clean with Katarina.
From grasp,phase rush and electrocute to conqueror, dark harvest, arcanecomet and omnistone.

With Katarina you can try every combination of rune, and they will eventually work (more or less). So unleash ur fantasy and try every rune path (yes, even press the attack work well on kitty kat).

---

---

This Item are just the same of what u can find everywhere. Im not here for this!!

---

---

Katarina is a great split pusher in this season 11. U can abuse this to become a little more like a yasuo main

---

---

Based on your build, you can choose what to do.

Split pusher: let those Iron 4 do an Aram midlane and abuse of that moment to take down objective on top and botlane.

Assassin: your Malphite engage in a teamfight 1v5? You just press E in the crowd and then ult everybody.

Tanky: Basically you will do what Malphite does in the previous story but you stay on fight until your enemy are all dead or most of their stun are wasted. Then u just go away to chase the single target.

---