Be nice, this is my first guide and i dont understand how to do a good guide.

This Item builds i shown are the builds i use. They works good for me and hope they work good for you guys.

Build 1: I start up with Doran's shield to stay on the lane because of the healthregen,armor,health boost i get from it. After that i buy boots and amplifying tome to get some extra damage on my abilities and some movement speed from the boots.
After that i buy a Rylai's scepter to get some slowing effect onto my abilites and more health and abilitypower. After that i upgrade my boots to sorceres boots for the magic pen and movement speed too. hextech revolver comes up next, its an awesome item it will keep you last longer in fights etc. zhonya's hourglass-abyssal scepter-rabadons-will of the ancient are the late game items all items will give you more surivability with katarina. i know that this is a expensive build.

Build 2 : On this build i buy boots and x3 healthpots but with this build it will be harder to lane. i buy mejai's and at 20 stacks you will have superb damage then i buy revolver-rabadons-zhonyas-hextech gunblade and void staff at last for the magic pen.

If you wanna play aggresive and risky, then pick Ignite and exhaust to pull of kills.
If you wanna play with one offensive and one defensive spell Pick exhaust and flash. With flash you can also combine with shunpo. Flash first and then shunpo to the enemy.

Cleanse is good against champs with CC's like Morgana,Sion,Taric,Lux etc

Katarina is a awesome bottom lane and top lane character also at mid. If your laning against ranged champs like ashe then i prefer going for maximize the bouncing blade to get minion kills and harrasing enemies. you should pick killer instincts pretty early especially against nunu,taric and nidalee because of their heals. Killer instincts+bouncing blade will make their healing reduced to themself. Try to lane until level 6 without dying it will make it easier later, In my oppinion i think that katarina is useless until level 6 but if you have the opportunity to kill someone then of course you should but dont take 50/50 fights.

Actually Katarina is really good laning with taric and sion because of their awesome stun. example: I tell Sion to stun someone. I use: Killer instincts-Shunpo-Death Lotus that will pick a kill, almost guaranteed.

When you and your team have gathered up and are prepared for a team fight, let someone else in your team engage the fight. After someone of your teammates have engaged use killer instincts-shunpo on the best dps in their team. It will make you take reduced damage from enemies. Then use Death Lotus directly after you have use shunpo. Katarinas passive is awesome too, after getting assist or kill all your cooldowns will be decreased by 15 seconds so u can use all spells again except Death Lotus. If someone on the enemies team tries to flee with low hp just shunpo after and then toss a bouncing blade. Sometimes you even will be able to use your ulti again directly after 4 kills/assists.

I pick some defensive runes like magic resist and health because Katarina is pretty squishy pregame but i also pick ability power runes per level and ability power runes because its nice to have some extra damage on bouncing blade and shunpo in pregame, i also choose magic pen runes because its awesome for Katarina. I pick 9-21 masteries on the survivability guide and 10-20 in the high ap build.

Spell Order : My favorite way is to maximize bouncing blade before everything else, But killer instincts is very good too pick it once then 1 times later before fully picking shunpo, but always maximize the shunpo before killer instincs, and of course pick ulti when you can :)