Hi, my name is samuelrw and I am not the best player ever lol. But I am pretty great with Taric, the Gem Knight, and would like everyone interested in playing this shiny champion to get some useful tips. Hope you enjoy it!

Taric is a tanky and very stylish support, that is considered a niche pick nowadays. His ability pool brings many advantages: heal, point-and-click stun, damage, armor buff, etc... He is definitely different from any support because instead of being excellent at doing an especific thing, he does decently many things. That´s why people don´t like him lol
Taric is not a hard champ to play, but it is somewhat difficult to be effective with him. I wanna help you :)

Pros

Tanky
Very good against ad comps
Armor aura
Punishes hard bad positioning
Ult with many functions (I will explain later on)
Heal
Good early, middle and late-game

Cons

Mana hungry early
Low range
Long cooldowns
Some problems against many AP casters in a team

The laning phase is the most important period of the game for a support. The support has to let the ADC farm safely, harass the enemies, ward and guarantee some kills. Usually, Taric lanes are safe and trading damage with the enemies can be difficult. However, a good Taric HAS TO attack some times, be in front of the ADC to protect and be always watchful for opportunities.
At level 1, the first skill to get is the stun (E), because it stops aggressive moves and can be used just to make the farming difficult for the enemy (stun their ADC when he/she tries to do last hit on a minion! It annoys a lot!. However, do not stun like crazy, because Taric is mana hungry early game.
After the E skill, get the "w" (armor aura) at level 2, so damage can be done to the enemies by activating it and, if their support is squishy or the ADC not careful, you can start dangerous and deadly (for them) moves! Use E to stun> walk into the stuned champion, use W for damage then come back. If your ADC is inspired and potions are available, Slow him with exhaust spell and chase him for auto attack damage. But this shouldn´t be done at level 2 most of the times.
After the w, get heal (Q). It costs a lot of mana and doesn´t heal too much, but it is ESSENTIAL for damage trade and saving the ADC in hard situations. Most of the Taric players fail because they think it is not whorty. Once you have all the three abilities that come before ULT, be always prepared for E the ADC> walk into him and W> come back and heal yourself and the your ADC with Q. OR E> W> exhaust> auto-attacks and some heal if killing is possible. Don´t be scared!
Once you reach level 6, it is way easier to kill or run away with your carry. Ult must be used to chasing and for fleeing.
Chasing: E> W> exhaust and ULT> auto-attacks. It does a lot of damage, the ad and ap buff from ULT is awesome and very hard to run away.
Fleeing: E and exhaust the cnemy closer to your carry> W> ULT if it seems unavoidable> Heal during the fight and after it.
I will explain about wards and first items later.

Sightstone with lens to prevent ganks and to ward dragon.
Boots. (ninja tabi if there is one or none AP carry at the enemy team
Glacial shroud for mana, armor and build Iceborn Gauntlet or Frozen Heart.

E (1)
W (2)
Q (3)
W or Q (4). Usually W.
W or Q (5). Usually Q.
Ult (6)
Several "W then Q"s. Prioritize W, prioritize Q only if your team is losing.

Upgrading E won´t increase the damage significantly and the stun duration remains almost the same.It should be upgraded for last. Prioritizing E is a common mistake that turns your heal useless.