Tutor / Trainer NPC.

Due to the nature of the combat mechanics and their associated learning curve, I would recommend a tutor / trainer NPC, with repeatable training quests offering low-level rewards (Salt, Flint - which I'd shorten to just Flint because calling it Flintstone just makes me think of Fred & Wilma) and relevant rewards (example: give Arrows as a reward for the Archery repeatable training exercise, but have the exercise itself give you a few that are only good for that exercise and enough to do the thing the exercise is for).

This should focus on every kind of weapon - knives, regular weapons like swords or hatchets, and heavy weapons like the greatsword, as well as the bow, and the explosive powder balls, etcetera. Exercises should give a mix of low-level rewards + relevant rewards if you do well. For instance if you get a gold star on the one for explosive powder balls, you get +2 explosive powder balls as a reward, perhaps.