Duels: Techniques & postures
Investing your skill points in Deflection and Dodge-type samurai techniques will give you many advantages in duels. This will allow you to parry more attacks, counterattack, and so on.
The Stone Stance is the only stance you need in the majority of the duels, as they're always fought with a sword. Be sure to unlock all techniques for this stance.
Some duels against Mongol generals will pit you against an opponent with a shield, fortunately the Water Stance is fairly quickly unlocked. Investing a few points in it will also be very useful.
Mythic Combat Techniques are also a great help once you've unlocked them.
The technique that allows you to come back to life in exchange for 2 bubbles of Resolve (3 in Hard Mode) can be useful in certain cases, for example if you are killed before having had time to heal and your opponent is low in life. Sometimes it's better to die and start the duel again, since you're keeping your current Resolve level and recovering all your life. Note that this is not the case in Hard Mode.