First of al thank you for watching this guide i hope it matches with your gameplay or can be helpful to modify your curret in order to play a better Syndra.
In this guide i will introduce you to Syndra, and will give you the basic tips needed to play her.
First of all and MOST IMPORTANT thing with her is Positioning. As her passive privides you with extra bonuses as the spells are casted at maximum range, using this will grant u a very usefull technique at every fight.
Dark Sphere, for example is Syndra's main & fastest spell as it refreshes every 3-4 secs, and it can be manipulated with Force of Will, Scatter the Weak, and of course her ultimate.
Force of Will, is extremely important when laning, and often it will be the first power to master because u can grab an alrready casted Sphere or an enemy minion, and throw it at a long range, doing great damage in long distances.
Scatter the Weak is a power that can work when attacking or defending. Why? Because it provides you with an stun if you can hit an enemy with and Sphere or you can know all enemies back in the range of the spell. Of course u can knock back and stun at the same time, though that is only recommendable when scapping, because you may lose them throw a wall... (Yeah it happened to me....).
Unleashed Power, hits 1 enemy champion with 3 balls plus all the balls that are arround Syndra when this spell is casted. It has a minimun damage and can be extremely powerful, i have reached damages of arround 900 (Magic Damage) without Void Staff.
NOTE!: YOU CAN NOT MANIPULATE ANOTHER SYNDRA'S SPHERES.}
Finally, u will find it really easy to farm minions because all of your spells (Except the ult) are in area.

As i mentioned before, Force of Will works with Spheres or minions.
The main tip with Syndra, or trick perhaps is: To Steal Blue.
It's pretty simple. My first back every game is at 6 mins (lvl 5 1/2 Approx). I buy the items i need and A WARD, i place it in the enemies blue golem and wait for 7:20 mins (Can change according to the enemy jungler) and as soon as the golem has about 300-200 life, i grab it with W, run away, drop him and kill him with Spheres and Scatter.
NOTE: As soon as u drop it, it will start healing and run towars his main position, so you must be fast!
AT TEAMFIGHTS, u can cast an sphere ramdomly, rush your ult towars the closest enemy and Scatter all the balls to stun the rest of the enemy champions, this is pretty difficult but a HUGE WIN if u are lucky enough.

Syndra's main problem are Melee fighters; Whenever a Melee champion approaches and you are not ready to fight, know it back and gain time, cause you will lose your passive bonuses and you cant run pretty fast to scape (305 basic, 375 with boots lvl 2). Remember that u lack of any Teleport like Kassadin or any movement of the kind.
Syndra's second problem are Nuke mages like Kassadin or LeBlanc. Syndra needs long fights to kill (Unless u are fed of course) and that's why facing Kassadin is a pain in the ***, anyway if you survive to the first rush of powers... u can Initiate your attack and kill the enemy with a correct Cast and Position.
Syndra, is pretty good against Ranged champions due to her passive and Supports, because they usually stay in the back. Ranged Champs like Ashe, can suffer a lot from Syndra's abilities making them suceptible during teamfights.

Well, this is basicaly an strong build that also allows u to stay in fight for a long time.
As soon as u start with Rod of Ages u can be pretty offensive with your Spheres as u have a pretty good store of mana and life. There is nothing to say about the Rabbadon's ... pure damage ... Rylai's is to maximize the slow u have with Force, and do some with the Sphere so it's easier to hit enemies, of course the extra hp is really useful too.
Abyssal Scepter and Viod Staff are to do some extra damage wiht Abyssal's & Void's Passives.

Perhaps u will suffer from some mana issues at first, as u have cd u cast faster and mana runs out really quickly. But u are much stronger in fights as u cast your Spheres with 2.64 secs and that allows u to create a massive damage in little time, and many combos faster. Here there isn't much to say... u cast fast, last long due to Rylai's and Will, and do lots of damage with Rabbadon's and the Void Staff, combined with theo ther items.

This is a neutral build, u have half of the allowed Cd (20% approx.) and a nice ammount of ap. Of course, Rylai's to last longer and do some slow while attacking.

First of all this build is made considering "Dark Sphere" (Q) As the main power.
As soon as u run into an oponent the idea with this build would be the next:
-1) If u can surpirse your oponent u should cast an Sphere in the bush, then grab it with Force of Will and cast it to them, as u do that u stun him with Scatter of the Weak and cast and Sphere again. Later u hit ult and u should hit him with 5 balls.
-2) While laning u can do 2 things: *Cast an Sphere and stun the opponent with Scatter, use your ult (4 balls) and then Force of Will, Sphere again.
* Also u can cast an Sphere, grab it, hit the opponent, cast an sphere again and the Scatter, use ult and u can hit with 5 balls
* Or u can Cast an Sphere, grab it and hit him with Force, use ult (4 balls) use Scatter and Phere again. As u used Scatter after ult u have no chance of missing the stun and u can stun incoming enemies too.
**Always consider using Force to scape as u can slow the enemy, or cast an Sphere and use Scatter to stun and run.

Here we have lots of Cd, therefore it will be really easy to dominate the lanes with Force of Will, here is what u can do:
*First of all, as u master Force of Will first, u can grab minions with no need of casting a previous Sphere, and due to the range it has u are free to hit without being harmed.
Strategies in fight will be the same, though u will be able to cast Force and Scatter much faster and that will give u a great advantage with a corret position.

Here we should aim to improve Force aswell, since we can cast fast and with a nice range due to our CD and the mana Regen provided by Mana Manipulator. Therefore, casting Force to initiate the fight, then an Sphere close to u and Scatter to Stun will be pretty effective, and easy to repeat unless u miss Scatter.