Of course context matters and will depend on what champion you're playing but essentially Kayn has a lackluster early game. He has no way to proc scuttle shield pre-form so ideally you want to be contesting and winning the first scuttle assuming your lanes have prio. Kayn also needs to be fighting early in order to get his form as soon as possible so you should always be looking for opportunities to counter-gank if you can predict his pathing.
The reason why Kayn is oppressive at lower elo is because of his fast clearing and ability to path through walls which can quickly outpace bad junglers and create an insurmountable lead.
Common starts against kayn would be to match the side he starts on and contest scuttle with a strong early game jungler(if he contests and loses he gets double scuttled), or if you like to play aggressive you blue/red/gromp and invade his 2nd buff