Sylas Runes explained
There's one set of runes for Sylas on patch
11.8
that is the clear favorite for LoL players and pros alike. The best Sylas Runes on the position 
Mid are Precision as the primary path and
Inspiration as the secondary path with a pick rate of 90%. Besides runes you should take a look on Sylas Build and if you are interested in pro matches take a look at Sylas Probuilds. If you want to discuss
Sylas then you should visit the champion subreddit.
Primary path on Sylas
Precision improves attack and sustained damage on Sylas troughout the match. Most of high elo players – and our LoL pros in the the major regions – have agreed that
Conqueror is the best keystone rune to run on
Sylas. This keystone rune provides additional power in the later stages of a game. As soon as
Conqueror is fully charged, Sylas deals additional damage and gains life steal. This is usually followed up by taking
Presence of Mind,
Legend: Tenacity and
Last Stand.
Presence of Mind helps Sylas with the mana problems by restoring missing mana, if a champion is killed. Sylas gains extra Tenacity with every additional stage of
Legend: Tenacity. With
Last Stand you deal more damage while you are at low health.
Secondary path on Sylas
When it comes to your secondary path, most
Sylas players prefer to go with
Inspiration.
Inspiration opens creative opportunities on Sylas troughout the match. On the
Inspiration path, the best runes for Sylas are
Biscuit Delivery and
Cosmic Insight.
Biscuit Delivery is a great rune for laning as it gives additional health and mana, which can help in more aggressive lanes.
Cosmic Insight grants summoner spell and item haste.