Against syndra, Watch your flanks and avoid walking through unwarded territory as Syndra has great setup with her Q and E combo. 

Do not let Syndra poke you down before a team fight occurs. Her goal will be to harass as much as she can before looking for a pick. Engage as quickly as you can so she is unable to poke you down.

Avoid fighting inside the jungle or around an objective as it will make landing her E and getting a multiperson stun easier. Fight in the open when possible and avoid grouping too closely. Against syndra, Watch your flanks and avoid walking on an unclassified territory because Syndra has an excellent configuration with its combo Q and E. Don't let Syndra take you down before a team fight happens. Its goal will be to harass as much as it can before you look for a choice. Get involved as fast as you can so that it can't bring you down. Avoid fighting in the jungle or around an objective as it will facilitate multi-person landing and stunning. Fight in the open air when possible and avoid regrouping too closely.