Weapons
You will want to use either great hammers or great axes. Great hammers provide the largest poise damage, but aren’t that plentiful depending on your primary stat. Strength for instance only has one. Halberds and great swords are ok, but definitely require more hits to stagger.
Facets
You have two options for weapon facets - blunt or reliable. They both give 5 extra poise damage, which is massive, but blunt reduces focus gain and reliable removes crits. I thought blunt would be the way to go every time, but honestly I really like reliable much more. The focus gen loss from blunt is very noticeable, and on bosses some of our biggest stagger damage comes from rune attacks, so focus gain really matters. Reliable as a name fits very well, because without the crits it makes everything much more predictable. I like knowing that a certain enemy will take the same amount of hits to kill every time, and that lets you plan out your kills in a group without any variation messing with your flow. Since two handers deal a lot of damage, a crit can also kill a mob before you would stagger it, preventing stamina and health regen from enchants, or messing with your flow when you expect a stagger to knock them out of range and require a gap closer to continue. The only reason I could see going blunt is on a crit capped stagger build, but I tend to prefer armor pen > physical damage > crit chance.
I also like the rapid facet on gloves to improve attack speed.
Rings
Increasing attack speed is very important for staggering, especially on bosses. Willow cap ring is a must.
Gems
Chipped and mottled granite every time. 6 poise damage is a ton. You might be tempted to go enchantment power, but making up for that 6 poise requires using stagger damage enchant, which at 15% is giving you 5.4 poise damage on a great hammer and 4.65 poise damage on a great axe before empowerment. So sure, with a mottled pearl, you would end up with around double the poise damage of granite, but you would have to forgo attack speed which will give you more stagger over time than the stagger damage increase, especially on bosses.
Enchants
Gloves
Gain 40 stamina on stagger on plagued gloves is huge. The great weapons are hungry hippos when it comes to stamina and this enchant will make it so you don’t have to regen often, if at all.
Gain 15% health on stagger on plagued gloves is also recommended. On trash you will be staggering non stop, so this can easily keep you alive if you find yourself losing health.
Weapon
I thought stagger damage was the way to go, but attack speed really is king. Most stagger builds are going to be using fairly slow two handed weapons and being able to squeeze more attacks in before you have to defend makes a huge difference, specifically on bosses. Add a durability enchant to make it more powerful.
Gain 15% health on stagger on plagued weapon is great as well, but the plague downsides on weapons are kinda brutal. I went with attack stamina cost increase personally, since there are a lot of things that make up for it - agility ring, jade ring, and glove enchant. Having this enchant on both weapon and gloves gives you a way to reliably heal on bosses without using food.
Chest
Focus Cost reduced by 25% for 10 seconds after Staggering an Enemy on plagued chest is pretty strong. It allows you to easily throw out 3 rune attacks on a boss after stagger.
Infected Enemy Stagger Resistance reduced by 30% on plagued chest is crap. The lifesteal from plague is useful, but I found that having to forgo 5-6 poise damage on the weapon to make it plague infused was not made up by this enchant. Health gain on stagger works well enough to not need the lifesteal.
Runes
With a focus on attack speed, Limit Break is very fast and does a ton of stagger damage, often staggering bosses all by itself. With enough focus gain, you can keep a boss permanently staggered by using this as it gets up from stagger. This comes off the strength weapon Gnarled Saw.
Poise Defense
Even with the focus on attack speed, being able to trade is pretty helpful. I recommend mesh as a minimum.