Hello! this is the first guide i ever made.
As Kata i always go mid, because she uses no mana that will make her stay in lane for longer than most mana champions.
Btw. Kata is my favorite champion ;)

Kata is very good at ganking, and should roam alot, try seek for a bot lane gank to help our adc to get fed for a win.

I choose magic pent runes. So i wont have to buy void staff.
I choose scaling health for more tanky
I choose magic resist so i take less damage in mid because usual mid champions is ap.
AP Quints for some starting ap

I choose 21-9 to make kata offensive and abit tanky.
i take 2 points in brute force because katas w and r scales on ad.
I take spellblade, because when u hit the mark from Q it gives a good bonus with Spellblade

To make Kata ap and tanky.
I buy Seekers Armguard early, because its easy to stack and gives good ap and armor
Sometimes u might need to buy a sight ward, to set and jump for a escape or to watch when jungler will gank you.

I max Q and W on kinda same time.
Because that will give most damage possibly.

As Kata in a fight i throw Q then jump with E and use W then Ult (in fights versus a strong champion or many champions at once)
U can also jump first then Q and W
Or even E>R>Q>W>E

Pros
Fun to play
OP Passive
High DPS
Good at multikills
Good mid
Good lategame
Easy to learn
Cons
Weak early game
Melee range
Needs the reset of passive
Gets focused
Hard to master

As Kata i play defensely and farm all minions possibly.
I go offense when the timing is to get a kill.