Flash + Heal

You should take flash + heal in 90% of your games, as it is very versatile with your kit and allows you to both disengage and engage better.

For engages, if your teammates manage to proc your passive on an enemy but you are just slightly out of range, you can flash + R to make up for the distance and ensure your passive stacks do not run out and allow the enemy to get away. If time allows, you can E first, but ensure that pathing will not mess you up and that your passive stacks won't expire.

As a disengage, you can use it in combination with your R to create a larger gap than other ADCs. By autoing a champion that is chasing you or hitting them with your W, you can then R to that target (preferably at the edge of the R circle to create the furthest distance) and then flash out. You can then follow this up with an E to create even more distance.

Heal helps you win early 2v2's, especially if you can predict when the enemy will commit to an engage (ex. you or your support is hooked by a champion) and you are able to heal before they manage to ignite you. It's also very versatile, as you can use the move speed boost to both disengage and engage from fights.

Flash + Barrier

The only time I really see this build being useful is if you have a Yuumi support, in which case the Yuumi will take heal + exhaust or heal + ignite. Since heal is reduced if you have recently been affected by it, it's a bit redundant to have two in a lane in which case barrier is the next best option to mitigate damage.

Flash + Cleanse

You can opt for flash + cleanse into lanes where the enemy has a lot of kill pressure due to champions like Nautilus, Leona, and Thresh (but NOT Blitzcrank, as you cannot cleanse his pull). Please remember that your 2v2 will be weaker as a result, since the enemy ADC may have heal instead of cleanse, which is better in the 2v2 since it allows them to take a bit more damage than you. Choose fights more wisely, and if you can cleanse appropriately this summoner can be better than heal in some situations.

It may be helpful to also remind your support that you have cleanse prior to the game starting, as sometimes people do not pay attention and this can result in your support thinking your 2v2 is stronger than it actually is.

Starting Items

Ideally, you want to start DBlade + 1 Potion, as the AD from DBlade allows you to hit your Q evolve faster. However, in lanes where it may be unsafe to walk up to auto attack, since your Q range is actually larger than your auto attack range, you may take DRing + 2 Potions for the extra mana, or you can take DShield + 1 Health potion if you feel you will be taking a lot of poke in lane (ex. playing against Xerath, Brand, Zyra).

Q + E Evolve + Explanation on why Collector is a Trap

Currently, even with the Galeforce CD nerfs, the ability to reposition yourself in fights, as well as use the GF active as a burst just makes it too strong of an item to not build. If the enemy comp has a lot of tanks, or your team is full ad, it may be beneficial to buy Kraken Slayer instead. Just remember that you won't have the leisure of GF active if you are caught out, and will have to use your flash.

You may notice that, instead of Serrated Dirk, I have put Pickaxe here instead to evolve Q first. This is because, in my opinion, buying Serrated Dirk and then building Collector afterwards on Kai'sa is a waste of gold. This is for a few reasons:

1) Runaans > Collector for Kai'sa's kit

Kai'sa kit has some magic damage in it, which the lethality from Dirk/Collector does not apply to, since lethality only ignores armor and not magic resistance. Runaan's passive also applies Kai'sa passive to EACH bolt, essentially tripling the rate at which you can apply your passive in teamfights (you do have to position well and kite for this, admittedly).

2) Runaan's is cheaper than Collector

It also costs 500 gold less than Collector, and after Runaan's second item, you ideally go for IE third item to get the IE passive powerspike, which nows gives you bonus crit damage at 60% crit rate (which you will have from your mythic + Runaan's + IE). This is where you use the Pickaxe you bought earlier to help you build IE, instead of building collector.

3) It evolves both your Q AND your E

I've been playing Kai'sa since her release, and I spent so much time trying to figure out the best way to buy items on her so that you could evolves both Q and E. E evolve basically turns you into Vayne, giving you invisibility during your E channel so you can reposition yourself better in teamfights. It feels really nice to have on Kai'sa, and since Collector does not give you attack speed, many Kai'sa players are essentially playing the game with only ONE ability evolved. This build allows you to have E evolve and Q evolve at level 10, which just feels so nice to have since the new item rework made it more difficult to do so.

Also, I see players sometimes building Dirk before they've even finished their mythic item. PLEASE finish your mythic first before buying a second Pickaxe. Mythics are a huge powerspike (GF or Kraken) and by delaying them you will be a lot weaker than you should be.

Late Game Build (W Evolve)

With S11, Zhonya's now gives less AP than it used to, which means to evolve your W, you need to buy Zhonya's and then buy the Blasting Wand for Nashor's. Less than ideal, but if your team could use some AP damage, then it is worth it to have. Zhonya's is just nice to have, since if you R into a teamfight and the enemy team immediately collapses on you, you can buy a few precious seconds for your teammates to turn on them. You do have to be able to land your W's to make full use of the evolve though, so keep that in mind as well.

Note that this build also lacks a Grievous Wounds item, so keep the enemy team composition in mind when using this build. If you see your teammates not buying a GW item, you may have to opt for the next build.

Late Game Build (no W Evolve)

This build is probably the standard for S11, seeing how prevalent healing is with Omnivamp now being a mechanic. Note that you should be buying Executioners Calling early in the game (potentially first back) in lanes against Yuumi or Soraka.

Levels 1, 2, and 3 you want to level Q + W + E. Level 2 Q + W with Hail of Blades as your keystone allows Kai'sa to get some really insane trades off early, as the W damage increases based on the number of stacks you have on the target. By autoing 3 times, using Q, and then landing a W, you can easily chunk most champions to 50% HP or lower.

After that, max Q first, then E, then R, then W.

Hail of Blades is super strong on Kai'sa for the ability to trade early and get ahead of your opponent in lane. Kai'sa is rather weak due to her shorter range, but by taking HoB you can make up for that by simply being a greater threat when the enemy is in your auto range. Taste of Blood helps with early trading, and Eyeball Collection/Ravenous are just the best options from the other groups to take, as increased AD and Omnivamp are very strong on Kai'sa.

https://www.twitch.tv/scrimm_na for League/non-League chill streams

If you have any comments/criticisms please feel free to comment and I will try my best to respond. Thanks!