Galio Runes explained
There's one set of runes for Galio on patch
11.8
that is the clear favorite for LoL players and pros alike. The best Galio Runes on the position 
Support are Resolve as the primary path and
Sorcery as the secondary path with a pick rate of 88%. Besides runes you should take a look on Galio Build and if you are interested in pro matches take a look at Galio Probuilds. If you want to discuss
Galio then you should visit the champion subreddit.
Primary path on Galio
Resolve empowers the survivability of Galio and increases the tankiness. Most of high elo players – and our LoL pros in the the major regions – have agreed that
Aftershock is the best keystone rune to run on
Galio. This keystone rune bulks you up, increasing both armour and magic resistance, once you immobilized a champion.
Aftershock synergises both with the sheer amount of crowd control Galio possesses and the need to be tanky as soon as you engage. This is usually followed up by taking
Shield Bash,
Bone Plating and
Unflinching.
Shield Bash powers up your tankiness and empowers your next basic attack while you have a shield.
Bone Plating make Galio overall tankier, by decreasing the amount of poke damage in the early game.
Unflinching inceases Galio tenacity based on your missing health.
Secondary path on Galio
When it comes to your secondary path, most
Galio players prefer to go with
Sorcery.
Sorcery empoweres abilities of Galio and increases the available champion resources. On the
Sorcery path, the best runes for Galio are
Nimbus Cloak and
Celerity.
Nimbus Cloak, which grants movement speed upon using a summoner spell, works amazingly well with junglers in particular as they take the shortest cooldown summoner spell,
Celerity boosts all movement speed bonuses to Galio.