Early Game:

In the early game, Taric is actually pretty strong. His E and passive allow for some annoying poke. You typically want to land your stun and capitalize on your enemy's immobility by using his passive to deal extra damage. Also, if you have Thunderlord's Decree up, that'll deal even more damage.
Once you get your W, you want to use it on your jungler whenever he decides that your enemy laner should suffer. Ganks will be a nightmare if your enemy lacks a good escape. Your W will allow a second stun to hit the other laner, dealing a ton of damage to a squishy. Also, Taric's ultimate can be helpful for a tower dive. I would recommend using it when you're already being aggro'd by tower.


Mid/Late Game:

In the mid or late game, you're going to want to focus less on doing damage, and more on helping out the rest of your team. You'll basically act as a second support. Your job will be pretty much the exact same a support Taric.

Pros:

+ Strong early game with his stun and passive.
+ His W works very well with his jungler, allowing for you to stun the enemy laner/jungler, even when your not close enough to deal damage to the target.
+ Is very helpful in teamfights with his ultimate and healing.
+ Despite not being a late game damage dealer, can still be a decent tank.
+ Taric is fabulous.

Cons:

- His damage falls apart late game.
- May require some early ganks.