Considering how difficult Kai'sa is to pick up and play...
...please do not play her in ranked until you have at least Mastery lvl 3 on her.
Now, I know this goes for pretty much every new champ/VGU released, but I'd say it's even more prominent on Kai'sa. Not only is she weak right now, she is also on about the same difficulty level as Vayne, if not a bit harder than her.
You really have to understand the battlefield, and where you're standing with her. Yes, positioning is everything with every ADC, but with Kai'sa it's even more important, due to her VERY low range, and the way her Q and Ultimate works.
So, unless your in Diamond or above, please do not play her in ranked until you have a solid amount of games on her.