This link is a great topic to really make great use of the DPS formula in PvE. General rule is that you should use as much ED% as possible as well as WD% on the weapon. Usually 3x ED% is a suitable number. Focus on a main element is key for high Dmg.
Also if it's flintlock build , investing in attack speed and APS is a great choice. Also using multi attack mythstones/legend affix as well as extra attack Mythstone is a great way to increase DPS output by a lot for flintlock ricochet since it's a primary skill . Also hero points can help a lot at 20.
Then you should most definitely use affixes like Push the Limit to increase flintlock MH% dmg as well as things like Glasscannon and/or Barbarian which can increase your DMG by 50% which is huge. As well as that, using ignore resist is a great way to deal dmg (as cheaper alternative to weaken but weaken is as strong or better ).
The crystal affixes are the most important parts of the build though as they're the most powerful as well as the set Affixes. I'd recommend 1x crit chance , 1-2x crit dmg (1 if you use rage set affix) as well as crushing blow for higher floors. Others can be regen or MP on hit as well as weaken and deadly strike .
Set affixes is up to you but for high Dmg, a great one is using Momentum but you'd need skills that boost move speed and move speed affixes on gear. Another one is demonic as it increases your dmg by 100% at enemies blow 30% HP which is like using relentless talent in some way. Combine relentless and demonic and you get great dmg.
Also set affixes such as Arcanist+Ascendant can be used together with weaken and Crits which can help you deal easily billions of dmg as the more enemies in the debuff, the more dmg you build does. Total Dmg 20% per enemy effected when crit.
The next sets can be the frozen set of the plagued set. The frozen set can make enemies frozen explode and each explosion is more powerful than the last by 125% and combined with frostbiting, you could easily deal crazy billions or trillions of dmg. Of course enemies need to die to explore so crushing blow is useful on very high floors.
The plagued set if you already have high enough poison dot dmg and cloud can increase the potency of the toxic cloud by 125% each enemy and with the blight legend affix, you can see why it's very powerful. This goes great with druidic set with regen as well as Arcanist and Ascendant. You can have it with Arcanist+Ascendant combo with druidic or one of the other. It's up to you.
A fantastic example is this build by @f00kee
Also a fantastic poison example which wasn't flintlock but could be tried with one is Poison Enchantress
There are many fantastic builds in the build compendium that can really teach you a way to deal crazy dmg.
Also this guide is useful in general DQ knowledge. The SHTT.