Went to do a Zandalar Heroic the other day and had massive issues. The group, all from the same guild and mostly in gear that was far higher level than my own, were pretty nice and asked me to leave. They didnt' kick or anything but told me to get some upgrades before trying to tank it again.
They handled it in such a way that I actually listened to their criticism's and want to work towards handling it.
Problem is, not sure really where to start, so if you guys coudl take a look and let me know what to fix, I would appreciate it.
Start off by sorting your gemming, yellow sockets should be Fractured Amberjewls, Blue socket's should be Fractrued Dream emeralds, and red's should fine ember topaz's. Use this to check you've got the right meta (usually paladins go for the Eternal rather than the Austere
There's a crafted 359 shield that shouldn't be too expensive these days the crafted 365 weapon would be good but can still be pretty pricey. The Mirror of Broken images from TB is an awesome trinket (don't let it's ilvl fool you this thing is a keeper), your armour trinkets are over budgeted, they provide very little real mitigation for that item slot. Impetuous Query can be wonderful (it's a 333 but its awesome non the less)
Talent wise I'd pull points from Judgements of the pure and Hallowed ground (get out the Habit of Consecrating) and put them in Reckoning, Pursuit of justice and 2/3 in Rule of Law. If you don't use WoG consider pulling a point from GBtL to finish off GBtL
Hit and expertise are, as of now, completely useless stats. You dont need them to be able to hold aggro, and though they can increase your dps, see them as crit or haste - doesent contribute to tanking per se. That said you have a painfull amount of threat pieces (hit/expertise is all over the place) and very little mastery.
As Teng stated, armor trinkets are very very very very very poor choices (I like to do some terrorism and say its the same as keeping the slots empty), and gemming more accordingly to the guide he provided would prove helpfull. If your looking for a better understanding for the motives behind these recomendations i suggest you read the provided link, or just fuss around for theorycrafting posts and guides, noone is going to write a 12 post reply here on HALP forums.
While you dont get better pieces to work with, try some reforging (i didint see any at all), removing threat stats (or dodge if the piece already has mastery) to mastery.