invest skillpoinst to combat style of your choise during level ups. You also should have chosen one of the combat skills as your tagged skill at character creation. Having high intelligence gives you more skillpoints per level. You can also find skillbooks to boost certain skills. Having high perception helps in ranged combat.
Edit: hopefully you did not choose 'good natured' trait at character creation as this lowers your combat skills. You could've also taken skilled trait that gives you more skill points but you'll get less perks(1 per 4 levels instead of 1 per 3 levels). There are couple people who can train you depending your stats and skills in arroyo. One trains in hand to hand and other in melee. You can also get sharpened spear in arroyo that is bit better than standard spear in combat.
As far as I rembember, there's no firearms in arroyo so it's hand to hand or melee