I ain't afraid of no host.
 Zealot Build - Warhammer 40k: Darktide 

Melee

• Heavy attack with melee 99% of the time.
• All activated attack damage stops at the first target hit and leaves you staggered for a second.
• Get good at dodging and don't activate your hammer until the horde enemies are dead or you 100% have a shot on something you need to remove for survival.
• Hammer has great CC and trash cleave.  During a horde, be sure to swing into piles of bodies every couple swings or you will get hit from behind.
• If you trigger Until Death make sure you get in a good activated heavy attack.  Even if you only hit a poxwalker, you will heal most of your HP.  If you crit or Chastise, you will heal to full.
   

Ranged

• Bolter kills anything except Demon Hosts.
• Less effective against carapace armor.  Blessings help negate that.
• Less effective against anything with no armor and a lot of HP. This includes hounds, though you have a good chance to stagger them.
• Even you slightly miss, you still have a decent chance to stagger.  Can be helpful for snap shots or if you get suppressed against bombers, snipers, and gunners.
• When using semi-auto, don't fire as fast as the gun lets you.  Let the sights come to rest.
• Don't forget about Chastise the Wicked.  It can replenish toughness and/or help get to cover.  Zealot can be really vulnerable in ranged with no toughness regen. Could be convinced to take Gloryhunter over Shattering Impact just to help with this.
• Hip fire can be extremely effective if you get swarmed by elites or need to save a teammate, just know how the gun kicks and make it count.
• Semi-auto is much more effective against hordes.  After you fire, enemies will likely cower, let more fill in before you take another shot so you can make use of the penetration and small AoE.
• If you are low on ammo (In general or in the mag), space out shots to stagger bulwarks, crushers, and maulers, tag them, and let your team take care of it.
   

Curios are all optional.

• More health and toughness are always good.
• Chastise the Wicked is extremely versatile, ability cooldown can help.
• Find what works best for you.  It ain't that deep.
   

Weakness

Main weakness is horde clear.  You can survive, but it can be extremely slow if you're forced to use the hammer the whole time and risk getting caught by a hound or trapper. If you try to spray into just a horde, you will eventually get caught with an empty by mag by something you can't deal with.  I will change out the bolter for a flamer if I know who I'm playing with, but with a PUG, you run the risk of getting pinned by a tagged sniper while no one else does anything.

 

The game in general

• REBIND YOUR TAG BUTTON TO YOUR KEYBOARD.  This goes for all classes and all builds.  If you can't tag enemies while surrounded, in the middle of a horde, with elites and a boss, while you are charging a heavy attack, uninstall.  Someone who could make that bulwark disappear in a second may be dealing with something else.  It's no one's job to babysit you.
• JUST BECAUSE SOMETHING IS TAGGED DOES NOT MEAN YOU HAVE TO TUNNEL IN ON IT.  Know what your build excels at dealing with.
• ALL ENEMIES ARE MORE IMPORTANT THAN BOSSES.  Enemies will body block hammer swings.  Ranged enemies will deal more damage while fighting the boss.  If caught by a trapper or hound and there is pretty much any other enemy type around, a player can be downed in a second.  Kill the mobs first.  If you know how to manage stamina and dodges, any class can kite a plague ogryn or beast of nurgle (and most melee enemies) literally forever given enough space.  Even if you are on a level with a condition that causes endless waves, know what you're built to do.  If you have great horde clear and terrible single target damage, plug a doorway try to eliminate ranged units.
• DO NOT USE MEDIPACK OR AMMOCRATE IN AN AIRLOCK IF YOU DO NOT KNOW THE LEVEL.  There's a good chance that door will open into an objective room with a loot room with a medicae station.
• IF A TEAMMATE GOES DOWN OR NEEDS RESCUE, DO NOT JUST TUNNEL STRAIGHT TO THEM.  They have a visible red health bar counting down to their demise.  It will not help if you charge in and get yourself downed, trapped, or pinned by a hound.  This is also a great situation to have a grenade stashed.