Don't waste your time, steal other people's!

Since Sylas has a pretty much op kit by itself, if you're able to itemize him better, you're pretty much going to be destroying the enemy team even in 1v9 scenarios if played more strategically.

When you're laning, once you've all gone through the level one team fight you'll pretty much have to go to your lane as soon as possible since you have to get to lvl 3-4 asap. Since Sylas is pretty squishy you'd have to wait for your sustain and farm safely until then, try to poke the opponent and/or try to evade trades since you're up to a loss in the fight in the most cases.Once you've got Protobelt and have gotten to lvl 4 (with lvl 2 W) once you shove to the tower your wave, you can start roaming through the jungle( i suggest best that you use your e a lot and go most frequently for your and enemy raptors) if the enemy laner doesn't have a fast wave clear you actually have time to get your or their red buff and back.
Once you get your Lich Bane and lvl 6 powerspike you can start enaging a lot more, once you get ahead(you won't have a problem with this in most cases) you can start ganking other lanes and snowballing them. Try to disengage if you don't have either of those up: Protobelt/Cleanse/Barrier/Flash in best case Zhonya too.