Build and Runes
Swain excels in teamfights and skirmishes that last for an extended period of time. Avoid this!
Make sure Swain is ignited or has some form of healing debuff on him when fighting him. This will let him heal significantly less from his ultimate.
Swain has pretty bad wave clearing problems unless he’s maxing out W first and even then it’s on a hefty CD. Play someone that can clear waves fast and force him to miss CS under tower.
Try picking mobile champions who are able to deal with his abilities.