Sorry, sure it’s been brought up a bzillion times but how should I be thinking here in terms of importance. Is it something like this? From most to least important?
Resists.
DA.
Armour.
Armour absorption.
Status affect mitigation (stun etc).
Reduce % damage affects.
Damage absorption buffs.
Dodge and deflect.
Fumble and impaired aim.
Block should be on the list someplace, but not current focus, no idea where to put that. Hit point pool too, again no idea where to place that.
This Information is already in the Game Guide here on this site, you should look there first when you want to know about gameplay mechanics.
DA is definitely #1. If you don’t have enough of it, you’re receiving crits all the time.
Armor absorption is #2, if you have less than 95%, you basically have no armor. The base 70% absorption doesn’t do anything for you.
Armor might be put here, but idk, armor is rather not important because not every build can focus on getting it without sacrificing anything. Don’t get me wrong, it is important, but a caster will never exceed 2k, if they build caster items, so this can be ignored in some cases.
Status effects only for Crucible and certain monsters. Stun is nice to have no matter what.
I don’t know if you mean reduce target’s damage or damage absorption for you character. Reduction for the enemy would be a must if you can pick a source of it not sacrificing much. For example, if you’re playing Soldier, you’ll always want War Cry unless your character is a kiter. Necromancer loves his Ravenous Earth’s first modifier, but if you can’t get it, it’s fine (although, I don’t believe you won’t have enough points to pick it, unless you’re a spellbinder, which sometimes has issues with points).
Damage absorption is rather only an addition. Only Arcanist has a huge amount of it in a regular skill, then there’s Menhir’s Bulwark, Primal Bond and Possession, which are all exclusive skills. Damage Absorption also stacks multiplicative.
Block, fumble and impaired aim are all RNG. I personally don’t like any of them and think they’re shit because my luck is so bad that I never, literally never get them in the right moment. I only pick Block if I play a character that can achieve a high % chance or is tanky/tanky as fuck. There are people that will tell you Fumble and Impaired Aim are a must if you can pick them, though, because they get them in appropriate times (if you’re one of them, I don’t like you! :p).
I think he meant picking priorities, not how they apply.
Yes, but the link to the game guide is good too. Thanks for the replies.
Ok, armour absorption I’ll up provided I can wangle it with the resists, DA minimum to aim at is 2.5k, better above 3k?
Sorry I meant damage absorption from Inquisitors Rune and the like, I know it’s applied last after everything else.
Currently my character will be praying to the RNG gods, high dodge/deflect with both Fumble and Impaired Aim in the mix, lowish armour and hitpoint pool. It probably isn’t a winning combination, but the beauty of Grim Dawn is fiddling around with the details.
From my experience, average of 2700 DA is the best. However, casters don’t really can achieve that much too often, so 2500 for casters is pretty sexy. Don’t reach for over 3200 DA, though, it won’t be needed unless you’re fighting Mogdrogen (can’t say anything about Crucible, I mean, I know you all aware of that that I am the best Crucible player in the world by just reading my signature, but I’ll let other people talk, don’t want to be the star here). I personally don’t like over 3k DA. 
Going to throw my 2cents in even thought i’m also quite new to the game but i learned some things dying.
USER_NAME_01 didn’t talk about resists in his answer probably because they are so obvious for experienced players that they don’t even think of them but as a new player i can tell you they should not be neglected. To me they are at least as important as Armour/Armour Absorption combo. Having them overcapped (higher than 80%) is also useful if you can afford it because many of the most dangerous enemies can reduce your resistances. The way resistances work, dropping from 80% to 60% doubles the damage you receive and some monsters can drop your resists by more than 20 points (but not many of them thankfully). Keep in mind there are potions that increase resists for a decent duration and you can use those to overcap critical resists for those dangerous fights so if you don’t mind a little preparation, a high overcap is not a priority (but is comfortable). Getting to 80% (or as close as possible) on every major damage resist OTOH is a priority. If you can increase maximum resist and have effective resist higher than 80% it can add a lot to your tankiness. Resistance to damage over time (poison, bleed, vitality decay and elemental damages) is particularly important. High resist to your own damage type (especially if it’s physical with Internal Trauma DoT) is also particularly important as some monsters will reflect damage back to you.
Talking about Armour. To put things into perspective an armour of 3000 with 95% absorption will protect you like an armour of 4000 with the default 70% absorption. After armour reduced the physical damage, your Physical resistance will further reduce it. All this means that you have multiple ways to mitigate physical damage and while you can obviously try to maximise all of them, if it means being totally vulnerable to poison you’re likely to die a lot in some areas (does being killed by flowers sound good to you 
). That’s not to say the advise to improve absorption is bad, all characters have a maximum armour they can achieve and any further protection must come from increased absorption. However if you have an easy way to get your base armour really high or can stack a lot of physical resistance (it’s much harder to acquire than most resistances) you don’t need improved absorption as badly. Look at the opportunity cost of each option and try to find the most efficient way to mitigate physical damage. It’s the most common damage type and some of the biggest hits you’ll receive will be physical so you need good physical damage mitigation but overlooking other resistances to get as much physical protection as possible isn’t a good idea.
Something you didn’t consider and isn’t strictly a defence but can definitely help your survival : ADCtH (aka life leech). Attack Damage Converted to Health will convert part of your weapon attack damage to health and heal you while you kill monsters. This is a very efficient way to keep at max health (or close) during prolonged fights. Unless you can kill everything really fast, no matter how protected you are, you’ll end up loosing health and you’ll need some way to heal yourself. Tonics of mending aren’t really reliable because of their long cooldown. There are multiple abilities that can heal you but ADCtH is definitely one of the most beginner friendly as you just have to keep hitting monsters and you’ll be fine. Note that relying entirely on ADCtH isn’t a good idea because if some monster stuns you or causes your attacks to “fumble” or otherwise prevents you from doing damage, you’ll die really fast. ADCtH works with spells that deal %weapon damage but doesn’t apply to spells with no %WD unless it’s part of the spell’s description (like Siphon Soul)
Another defence that could be added and isn’t obvious at all is player piloting skill. If your character is dealing a lot of damage over time, you can keep moving without loosing much damage output. If you’re good at dodging attacks (not every attack can be dodged, but many of the most dangerous can) you can live with lower overall defences. If you want to “face tank” everything you need to be a lot more tanky.
In the end i’m not sure there’s a definitive, complete, priority list. It will depend a lot on your build and play-style. A character with a really high HP pool and lots of ADCtH can easily survive while taking some heavy hits due to lower physical damage mitigation but needs stun and freeze resists really badly to keep hitting things. A character that relies a lot on moving and not being hit definitely needs trap resistance. What everyone needs is enough DA, Resistances and Physical damage Mitigation to avoid being one-hit killed.