Syndra forces you to take a wider look at the battlefield.
You can't just focus on champ you want to target/champs in the team fight. You need to be aware of where your previous balls have been placed, and for optimal ulting, how long they have been their for.
It's tough to do well with that.
What's easy, is throwing balls at people in lane. She is a massive lane bully. Just watch your mana.
Best trick to learn with her is the instant 2 ball stun. Not instant for you, it requires a little set up- but if timed well, it's instant for the enemy.
Say you're a midlaner, and you're ganking bot lane. Half way down the river, throw a ball out in front of you. Walk past it and as it's nearly out of range of your W, pick it up.
Now, walk into lane, throw your W in the direction you want to E, and simultaneously put a Q next to it. Then E.
Makes for a pretty undodgable stun and great for ganking. Follow it up with you Ult and someone's getting sent back to the fountain.
A lot of Syndra plays like that. You need to be ahead of the game to set up your plays. Which can be tough.