This is not a beginner guide. You need to have a few things unlocked.
These are Mandatory:
Mist's Secondary Traveler Memories: Flèche & Parry.
Essences: Overload, Insight, Wealth, and Divine Faith.
You also need to pump enough Reverie into Mist's Star Trail to unlock Light Damage as her main damage source on autos. This procs Essence of Flow.
Early Game:
As you begin your run you will want to Invest any dream dust into upgrading your Flèche and Passive. Keep them equal +3/+4/+5.
Use anything you find that could be useful in your progression.
Essences: metal/momentum/regeneration on Flèche instead of the options I've chosen. Momentum is very strong if you get it to 1s+.
Efficiency/direness on parry
If you cannot find Arrow Storm in it's place an Umbral Sword or Flaming Whip works.
If you find overload early, put it on a memory that you don’t use.
Money-gen Tips:
Place the Wealth essence onto the Flèche Memory if you don’t have Spiral Essence. We want to level wealth to 500-600% quality as soon as possible to maximize gold generation and give us good economy. Allows us to buy/dismantle low tier memories from shopkeepers for additional dream dust. High tier memories distill at the Purification Altar.
Overload + Direness + Efficiency will grant you near perf parry uptime but there will be downtime where you may be susceptible.
Flèche has a built-in sustain mechanic (on-kill) however It is doubly important to always have an additional form of heal because there are mobs that severely limit our sustain. In addition be weary because there are game breaking bugs. In the wild currently is one that while Parrying your health may be set to 1hp.