Ok, there's a pretty easy flow here. It's pretty unnecessary to list all the things because for the most part they fall into a specific set of buckets.
- Apply static Damage reduction first. If you have a static value reduction for damage, that gets applied first.
- Apply shields next. The arcane ward is the only example I can think of, but if you have some kind of shield, it applies here.
- Apply resistance. If you resist a damage type, halve the remaining damage.
- Temp HP next
- Finally your actual HP pool is drawn from if there is any damage left.
Now lets look at the backup for why this is.
Resistance and then vulnerability are applied after all other modifiers to damage (Player's basic p75)
So we know the order for static damage resistance (a direct modifier to damage) and straight resistance (applied after modifiers).
The other things modify how damage affects you not directly the damage, so they are applied in a different order.
There's a bit of a finicky point here with the arcane ward. The D&D designer intent is for it to be applied before you apply resistance:
If an abjurer has resistance, it is applied after the ward takes any damage. (Jeremy Crawford)
This is a bit odd, but since the ward functions like static resistance (though I'd argue it also functions something like THP), it's considered a reduction of damage and thus is applied before resistance is applied.
THP are dealt with before you deal with your regular HP so the rest of this follows.
