Never try to fight him 1v1 until very late in the game (unless you're Jax, Yi, Fiora, and maybe some other duelists), and even then only as a carry. If you look at his abilities, it's all single target damage / healing. That's his specialty. He loses a lot of power when teamfights start because it's easy for one person to interrupt his ult.
Never sit around in lane with less than 50% hp.
If he's low hp do not try to facetank his autos and finish him off. Make sure he's stunned or you're kiting him. He heals a lot of health from each autoattack when he is low.
If he's chasing someone who is low or you, whacking him will temporarily remove his movement speed buff.
Get QSS to remove his ultimate if you have problems dodging it. Get merc treads. Around half of his damage is magic.