Play safe early on, focus on bailing your adc out rather than setting up plays, kench doesn't have the mana for sustained combat in early lane. Focus on farm, you may have to steal from your adc a bit. use devour at times to damage the enemy team, (accidentally hitting minions along the way). As much as an adc needs farm, so do you since you won't be building sup items. Late game you are the engager, Swiftness boots reduce your slow when you have eaten people and you won't catch anyone without them, it's imperative that you buy those boots. Kench is slow even with alacrity swift boots on, so stay in range of your team during all pushes. Don't buy guardian angel on kench, while it's a cool item to have, it's not worth 850 hp on this monster. Summoner spells are personal preference, but I find kench lacking hard in mobility, and flash/ghost a necessity to fix that.