As jim says, CON and DEX are the best stats to focus on. Even if you're using heavy two handed weapons, two points of strength is sufficient. Maybe you can justify a third if you're using warhammers but I don't recommend it. Grace is okay. Definitely get at least one point one point to power up your will and perception for cheap. I like to get two. Three might even be worthwhile if you're investing heavily in song or smithing, but I haven't tried it enough to say.
I don't know about archers, but for fighters your best methods for dealing as much damage as possible are either two handers or a one handed weapon with both finesse and subtlety. Damage generally matters more than accuracy because late game enemies have insane armor values. You literally won't be able to harm them if your attack power isn't rock solid.
Weapon damage follows the usual XdY format. One point of strength increases damage sides by one and critical hits increase the number of dice. So if you have a 2d5 damage longsword, and you have at least one of strength and it weighs at least one pound, its damage becomes 2d6. If you crit with a 2d5 longsword its damage becomes 3d5. With enough accuracy you can score multiple crits on a single attack, so that same longsword's attack power could become 4d5, 5d5, etc.
Heavy weapons can crit too, and it's not a bad idea to use a two hander and build for crits. The difficulty of scoring a critical is based on your weapon's weight, so lightweight bastard swords are a good choice. Some enemies are protected against critical hits, so even if you're running a subtlety build, keep a heavy weapon around. Armor penetration is the holy grail of weapon effects to such a degree that a penetrating dagger can outperform a greatsword without crits.
On the defensive side, the dodge in the evasion tree is available right away and it's really good. In a fight, alternate between attacking and moving away to get the bonus mostly for free. It also helps a lot when running away and dealing with archers.