the Exhaust can be traded for Ignite if you want your lane to have more kill pressure but as always flash is required.

The flat armor is recommended to lessen poke from the apposing adc.

The scaling MR can be traded for Flat MR if you are against a high damage ap support ie Annie or Karma

The Movement speed quints are best IMO as it helps to run around warding, and helps you move to throw your lantern to help allies.

Now the Magic Penetration marks help poke and deal damage, however they can be traded out for things such as mana regen (if you have that problem), a defensive stat if you decide you need it, or for anything else this is fairly flexable.

Go 0/12/18
Resolve Tree
unyeilding for more tank stats
explorer to help roam and create pressure
Veteran's Scars to help early game survival
Perseverence because insight is not really needed, flay and hook is plenty to cc and peel
swiftness so you remain mobile in a team fight so you can lantern and peel
Bond of Stone Because it is a great increase to durability and Grasp of the undying is more for Dedicated Tanks whom attack lots

Cunning Tree
Wanderer to create presence
Secret Stash b/c it is all that is really relavent for supports
Meditation b/c you are not focused on Damage
Bandit for Gold Income

Start
First Choice is Coin or Relic Shield, build Coin if your team needs a disengage or engage, ascention helps this HOWEVER if building relic shield later you can build righteous Glory for an extra engage.
Lane
Your first goal in lane is to purchase your sight stone buy this and get a sweeper
typically after sight stone i will upgrade my gold item to level 2 and then get my mobi boots.
Mid Game
from my experience tank thresh typically just does more for the team so after lane I recommend building tank, if the enemy damage is AD frozen heart if it's an AAer, randuins if not. then if AP locket if the back line is having a hard time surviving, banshees if you are in the middle of the fray

early point in flay allows for disengage and extra poke due to the over time AA damage increase but maxed last simply because the other skills provide better utility

Maxing Death Sentence First because the higher the level the shorter the CD so then more HOOKS

Dark Passage maxed Second as it helps your teams ability to escape and survive

The Box is naturally maxed ASAP when at the normal levels

Laning

Level 1 flay the minons to push them in in an attempt to hit 2 first, if you succeed in hitting 2 first use the threat of your hook flay combo to bully the opponents back, this is most successful when you have a marksman that is strong early game. when continuing laning i typically will place my green ward in the river bush either if we have pushed up or if you believe the jungler will approach bottom soon. on b's if you dont have a sight stone buy a green.

Mid Game

first i recommend buying a pink and placing it in your team's defensive bush north of the dragon pit, (ie purple side down the hill just north of the lone bush blue side up the hill in the bush behind red buff)

the key concept to understand is that you want to ward areas where enemy players will walk through often(duh right?) the other key idea is that you want to keep your objectives warded, with those warded your team can take them when the enemies are on the other side of the map and your team can move to contest when the enemies are taking it.

TEAM FIGHTS

so the assuming all of your skill shots land the way you intend to what you want to do is stay on towards the front line while the two teams are dancing apart from each other and hook an enemy carry if they step out of line. once the fight has begun your biggest role is to peel for your carry whether that be your AP carry or AD carry does not matter just keep them safe.

Your flay is will possibly be your most useful tool because it can knock back a large amount of champions who will try to go in on your carrys while they are mid ability (ie leona e)
the q is useful in team fights because if you land it it will stun the enemy for a brief time and also allow yourself to pull yourself into them and flay them away.

HOOKS HOOKS AND MORE HOOKS
Hope you enjoyed my guide

have fun in summoners rift