Syndra is a very high damage burst mage. All of her spells have a very large range and are adept at poking and harassing. I hope this guide is helpful.

"BY FORCE OF WILL"
-Syndra all the time

Your main goal as Syndra is to GET FED and stay safe using your massive range. With no real escape, positioning is very important.

"IMPRISONED NO LONGER"
-Syndra all the time

Pros

1. Very large range
2. Adept at kiting
3. Long range and powerful CC
4. Amazing single target damage

Cons

1. Very Squishy
2. Difficult to play

"EASILY"
-Syndra all the time

Syndra should try to focus on getting cs, while also poking aggressively. Poke your enemy back to their fountain, or if you are feeling confident go in for the kill by initiating with a Dark Sphere pushed by Scatter the Weak. If you are playing a game where you become the target of a gank and you don't have enough hp or mana, you wont have a reliable way of escaping if out of position. You can stun multiple enemies at the same time with scatter the weak, but if you don't have enough time and are getting dunked on by a Rengar or Kah'Zix then simply pushing the enemies away with Scatter the weak can give you enough space to leave, if they've already casted any gap-closers.
Its very important to watch your mana when going in or dealing with ganks.

"People fear what they cannot understand"
-Syndra all the time

At level 13, the scaling runes have become stronger than the flat ones. With full cdr your dark spheres will have a 2.4 second cool down. SPAM THEM. Your brand new fancy Seraphs Embrace will effectively give you a little over 120 ability power, with your deathcap, deathfire grasp, and hourglass, you will have well over 500 ap, and a massive, quickly regenerating mana pool. The active from your Seraphs Embrace will help with survivability in teamfights where the enemies focus you.

"Run, playthings."
-Syndra all the time