Zilean Runes explained
There's one set of runes for Zilean on patch
11.15
that is the clear favorite for LoL players and pros alike. The best Zilean Runes on the position 
Support are Resolve as the primary path and
Sorcery as the secondary path with a pick rate of 49%. Besides runes you should take a look on Zilean Build and if you are interested in pro matches take a look at Zilean Probuilds. If you want to discuss
Zilean then you should visit the champion subreddit.
Primary path on Zilean
Resolve empowers the survivability of Zilean and increases the tankiness. Most of high elo players – and our LoL pros in the the major regions – have agreed that
Guardian is the best keystone rune to run on
Zilean. This keystone rune grants a shield to your teammate and towards your own, as soon as one of you gets damage by an enemy champion. This is usually followed up by taking
Font of Life,
Second Wind and
Overgrowth.
Font of Life provides your teammates with more sustain by healing them whenever they attack a champion whose movement you've recently impaired.
Second Wind powers up your sustainablity in lane by healing after taking damage from an enemy champion.
Overgrowth increases your maximum amount of health.
Secondary path on Zilean
When it comes to your secondary path, most
Zilean players prefer to go with
Sorcery.
Sorcery empoweres abilities of Zilean and increases the available champion resources. On the
Sorcery path, the best runes for Zilean are
Transcendence and
Manaflow Band.
Transcendence for some more Ability Haste. This is usually followed up by taking
Manaflow Band for additional mana and mana regenaration.