Avoid playing her into any assassin if you're bad at her. Be careful of long ranged mages like Xerath or Ziggs too because they're difficult to go against for a new Syndra player too.
Do not spam her spells early otherwise you go out of mana, only harass while farming, or if it's a favorable trade. Care about the spheres you placed so your ult is more powerful, and ward everywhere around mid lane because Syndra if weak to ganks, especially if her stun is down.
Also have fun