Get these to L25 ASAP:

Boyarsky’s Chip: Lol. +Thorns. Nothing to explain here. Dump as many points in this as you can, but make sure to get the L25 bonuses of the next 2 gems.

Bane of the Powerful: Creams elites, helps survive against them and doesn’t scale much past 25? What a great early investment.

Bane of the Trapped: “How do I trigger the slow!?”, easy – get in their face.

Temporary defensive gem? Ehh… Molten Wildebeest’s Gizzard may be the best in this phase of the game…? I wouldn’t mind using it and leveling it up to 50 then augmenting it.

These three gems will last until you get into some ridiculously high GR’s. In which case, check the next tab.

Any other gems worth it? 

Bane of the Stricken: I don’t know if you’ll ever need this, but when you hit the high 70’s you might consider it. If you find yourself taking more than 1 minute to kill yellow elites – it’s time to switch Powerful to this.

Esoteric Alteration: Is the late game defensive gem of choice.

Boon of the Hoarder: You need this for speedfarming.
(See: Speedfarming General, Crusader Speedfarming, Best Crusader Speedfarming Build)

Aside from these 7 gems listed in these tabs, any other gem is considerably worse.

What’s there to say? Plant your feet in front of your target and slug it out. 
Align your cooldowns to all come out during Iron Skin!
Hunt down elites like a madman!
That’s 90% of it!

Elites – they’re your best friend. Since our AoE damage is poor (yeah, Bombardment owns now, you’ll see how bad it is later on), it makes no sense focusing on whites. If you haven’t played a character wherein elite hunting is your priority, this may feel weird, but try it out!

Align the stars – Iron Skin  is your best skill. It quadruples your damage. Make sure you can use the entire duration, and all your Thorny skills are on cooldown! Make it a habit that you HOLD OFF on using, example… Consecration, and wait for Iron Skin to come up. It’s a very bad habit to WAIT for Consecration when Iron Skin is up.

Align the cosmos – It doesn’t stop there. Convention of Elements? Triples our damage on top of that. Provoke + Spiker? Double it again. You get it.

Elites + Aligning – once you actually try it and see how powerful it is, you’ll know why even the hardiest elites in the highest of GR’s will be a juicy target.

So don’t complain about Invokers lack of AoE when clearing rifts. Yeah, it’s a problem and puts a cap on speed at the low end – but you can easily farm higher GRs as compensation for this. Not every set can do everything.

Resource gain and Wrath related changes are 100% irrelevant for Thorns of the Invoker, which uses none of it.

Damage? Ahh.. let me count the ways! While there are many ways to improve Thorns damage (many of which are recommended in the base build) let’s run by them.

Thorns: is your bread and butter. Increased by the substat. Strength modifies it. Iron Maiden (Passive) boosts it by 50%. Attack Speed indirectly improves it. CDR is huge for our cooldowns! Blocking improves Thorns! There are many vectors to improve Thorns (and how it interacts with Invoker), directly or indirectly!

Fervor is great. Attack speed and CDR? Really!? Finery improves Strength! Lord Commander is mainly there to reduce the cooldown on Steed Charge. It improves your farming speed greatly. Bombardment-CDR is a bonus.

How about ways outside the base build?

Well, now it goes into the territory of “Practical” increases which are worth the trade off. While I can’t advise you what’s worth it or not given that everyone’s setup is slightly different – here are some ideas…

Akarat’s Champion is sick once you’re able to use it consistently. It requires massive CDR. Use Prophet – it’s a significant survival tool later on. Akarat’s Awakening is great to help you on this front.

Laws of Valor-Invincible is a great hybrid choice. Always keep it in mind. It gives decent attack speed bonuses and its active not only further boosts ASPD but gives a significant Life per Hit bonus.

Fanaticism and Holy Cause are “small” bumps in your DPS.

Lord Commander may be in and out of your build. Again, it’s main upside is SPEED which you can drop sometimes for tryharding GR’s. But, in the “elite killing” game, speed means a lot.

Defense is usually self-healing and/or damage reduction.

Well, we can’t really talk about ALL the ways Crusaders can increase survivability, can we!? Hell, Iron Skin is our best offensive cooldown, and gives a hefty defensive bonus!

Life per Hit is goes a long way to help you survive. The 6pc attack speed bonus synergizes well with it. While only Laws of Valor-Invincible is the only built-in Crusader source for it, rolling it on weapon (amulet) is a good choice.

Laws of Justice-Immovable Object is the king of hardening.

Indestructible is a great passive. It nearly ensures you can kill ANY ELITE every minute. It gives you a second layer of insurance that your mega alignment of cooldowns doesn’t go to waste.

Invoker and Thorns doesn’t use Crit as a stat – so your main advantage is that you have so many EXTRA ROLLS for defense! It can be argued that AS and CDR replace these stats… But AS and CDR increases our defenses indirectly! AS gives more life per hit, CDR gives more mobility and usage of cooldowns. Attack Speed and CDR, while most builds ignore them, these are great for Invoker.

Mobility and Speed are a luxury as a fresh 70 character, but here it is anyway:

Crusader’s Steed Charge is a very mobile skill, but it’s part of our main offensive skills too… it’s a bit of a problem I admit. Most of Crus mobility is locked behind items, but you can make a few changes for bounties if you’re desperate for speed.

Lord Commander: Reducing Steed Charge cooldown is legit. You can even try using the Endurance rune if you’re hellbent on the anti-elite strategy.

Fervor reduces Steed Charge CD, and you can even change the rune to Endurance if you don’t need Spiked Barding.

Any other changes for speed at this point is too greedy, and I can’t recommend it.
(See: Speedfarming General | Crusader Speedfarming | Best Crusader Speedfarming)

Belt: Is the first place I’d dump shards on. Belt of the Trove helps us with our AoE clear PASSIVELY (which is relevant in the early game) but more importantly, triggers our Bombardment for free, and gives our 4pc 100% uptime. Goldwrap and other semi-useful fillers are found here, too. Once you get Trove, you can even remove Bombardment from your bar…

Chest: is next. Aquila Cuirass is a free, brainless 50% damage reduction. While Heart of Iron is also in this pile, it’s only considered a filler – the actual Thorns damage you get from it is small.

Bracer: We love elites! So we love Nemesis Bracers. It has no effect on our combat stats but it helps farm faster.  (Don’t even think of Sanguinary Vambraces if you find it – the proc is slightly stronger than 1 Punish)

Shield: isn’t a bad place to invest. While the possible pool is huge, Vo’Toyias Spiker and Akarat’s Awakening are no joke. The best place to spend when you’re done getting the above items.

Other filler items? To be honest I don’t think there’s much out there. String of Ears… Leoric’s Crown… Illusory? Nothing game breaking.

Reminding you of the bounty rings:
– Ring of Royal Grandeur: Act I bounties, to fit all our greed.
– Avarice Band: Act III bounties, for speedfarming.

There isn’t a “right choice” here. If I’m to recommend one at gunpoint… it would be upgrading 2H Mace for The Furnace. Why? There are only a few weapons and shields that are even remotely usable by Invoker. Furnace isn’t “that” hard to get, given the small pool of possible results.

Upgrading 2H Flail and Shields to attempt completing Norvald’s Set (Flail of the Charge, Shield of the Steed). This vastly improves our speed. Shields will also yield Vo’Toyias Spiker which is amazing. It works on our Punish-Thorns.

Upgrading Axe for Hack ~ meh… it really isn’t as good as it sounds. If you get one randomly, yeah why not – use it or cube it for the meantime.

Daggers for Pig Sticker: while this is the ultimate weapon for Invoker, it only shines when augmenting a “Fully realized build”. Since you can’t improve a turd, our resources are better spent getting us out of turd status.

The Classics: Good for any type of newer character, and even the most battle-hardened of builds.

Ring of Royal Grandeur: “Break” your 6-piece to make space for a good filler item!

Accessory Sets: Traveler’s Pledge is about as good as it sounds for a build that wants to walk around hunting for elites and bashing their face toe to toe.

Convention of Elements: Good ‘ol CoE. Wear it, Kanai it, as a filler or till the end of time. Learning to maximize CoE in any build you choose is a turning point for higher GR’s.

Unity: Straight 50% damage reduction in the cube. Too bad you need two of ’em.

Goldwrap + Avarice + Boon of The Hoarder: I don’t care how many times I have to remind you about this combo. Be on the lookout. Avarice drops from ACT III bounties.