To efficiently level up your characters and grind for skill points, focus on areas with high monster density and good experience rewards. Early on, simply fighting monsters around your current story objective is sufficient. Once you unlock Alltrades Abbey, consider the following:
- Metal Slimes: These rare monsters (Metal Slime, Liquid Metal Slime, Metal King Slime) give immense experience. They have high defense and often flee, so use abilities like 'Thunder Thrust' (Spear skill) or 'Hatchet Man' (Axe skill) which have a high critical hit chance, or 'Metal Slash' (Sword skill) for guaranteed damage.
- Grottoes: In the post-game, high-level grottoes are the best source of experience and skill points. Repeatedly clear grottoes that match your party's strength.
- Vocation Switching: When grinding skill points for a specific skill tree, switch your character to the vocation that grants those points. For example, if you want 'Courage' points, play as a Warrior. Once you've mastered the skill tree, you can switch back to your preferred vocation, retaining the benefits.
Remember that skill points are awarded based on the number of battles won, not necessarily the experience gained. Therefore, fighting many weaker enemies can sometimes be more efficient for skill point grinding than fighting a few strong ones.