To run combat "OSRFix" style, the following conventions are applied.
Note that this is not terribly specific to a certain rules set, and could be applicable to almost any OSR compatible game.
This is more or less a "snap shot" of how I like things to go, at this particular moment in time.
Rules in use:
Non rolled initiative
All weapons and most monster attacks inflict 1D6 damage. Powerful monster attacks are given as additional D6.
A damage roll of a 6 always inflicts an injury. Healing times can be determined using the recovery table.
An attack roll of 20 always hits, and inflicts a situational or brutal critical in addition to any hit point loss.
An attack roll of 1 always fails, and the character suffers a situational critical.
Characters reaching zero hit points can be "checked" by any character taking 1 round to do so. Roll on the "death" table. If not checked, the roll is made after 10 minutes (1 turn), for example if the character's body was abandoned.
Options depending on whim:
Weapon vs Armour to hit modifiers when fighting humanoids.
When declaring actions, the player rolls 1D6. Roll of 6 gives a bonus snap action. Roll of 1 means character acts last but will get +2 to all defenses during the round.