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Tactics are a very useful skill, but personally, I only level up tactics when I'm playing as Haven. Otherwise, I play solo, and it doesn't matter what my morale or luck is; it's always positive.
Which skill should you level up first: melee or ranged combat? I think it depends on the enemy. Sometimes, ranged combat can help against ranged units and lightly armored units that won't let you get close, thanks to their long-range attacks. If you level up melee, it's not that useful until you reach the enemy, especially if they're ranged. You can lose a lot of HP, and then you have to be glad if you have a potion of immortality. But, it's up to the player to choose which skill to level up first.