Overview
This is my build where as a new player i hit mythical glory with playing kimmy most of the times and with a winrate over 70%.
Classic Build
I personally dont like sky piercer because its so popular right now so someone will definitely build that item but if no one does you can think of buying it after finishing boots + Concentrated Energy. Concentrated Energy is a must in solo queue. It gives you insane sustain in laning. Feather of Heaven increase your dps by almost 2 times and i really recommend it buying it but sometimes you need to buy glowing wand vs other comps. Holy crystal as 4th item is great way to incrase your dps but if you have an enemy team that requires huge utility items then you can avoid picking this but still you should pick it. Divine glaive is an amazing late game item you should buy unless for some reason the enemy comp is 5 squishies. After you finish first 3 items you can try to 1v1 any marksman in the game but for the end game you still need divine glaive if you need to shred tanks. Last item is completely situational. Sometimes you want to buy sky piercer as second item so you can buy feather of heaven last. Sometimes you need to buy glowing wand, athena, wind of nature, blood wings even demon hunter sword is good right now. Here's few build i recommend:
Sky Piercer Version
High carry potentional build i dont recommend this build if the enemy comp is full of assassins.
Crit Kimmy
I know this build might make 0 sense but if the enemy jungler is an offtank fighter like lukas leomord maybe fredrin and you feel like you can 1v1 enemy mid or marksman easily this will shred them into pieces.
Mage
You should always run mage amblem + Thrill to get 46 magic power before the game starts otherwise your early game will be weak. For soloq and 90% of the times weakness finder is the best one but if you have well coordinated team with crowd control effectts, war cry is an option as well.
Battle Spell
You should take purify vs some matchups like tigreal etc but most of the times flicker is better since it provices offensive and defensive options
Mid Lane
If you play with the runes I just showed you should push mid lane as soon as possible and then play with your roamer and jungler. Try to take 3v3s as much as you can kimmy is insanely overpowered in the early game. In mid game thing might get started a little bit bad for you but this is where you have to decide your build after holy crystal. If the enemy team has too much threat for you should definitely think defensive items like wind of nature athena etc but if you think you can zone enemy team then go for full damage. In late game you should already build divine glaive by now and you have to realize that you are insanely strong with your team and you can defend base like chang'e. Just try to focus your positioning and everything should go smooth if the enemy squishy has no dash (champions like layla cyclops etc) you can start fight with your ult into second skill and you should guarantee that kill.
Gold Lane
Kimmy is more terrorizing in gold lane but some matchups are borderline unplayable. Considering the fact that your enemy player has also a brain you should avoid those matchups: Lesley, Clint, Brody But if you are a low mythic or legend player you will most likely play versus moskov (marskman emblem not fighter) hanabi and layla players which are extremely easy to beat as kimmy.
Best With Khufra
100% co-op win rate
Roamers usually play with mid laners so khufra is extremely strong with your ult range and second skills basically you can ckill anyone in the early game its even better than ixie + diggie combo but this syngergs often relies on khufra player's skill.
Watch Out For Gusion
20% counter win rate
You should always ban gusion because they can overkill you easily so even athena wont save you most of the time.