1. Goto Display Options and set the combat display to "path only" or "none."
2. React REALLY FAST and accurately, and don't get hit. All that's needed to block is tilt at 90-degree angles to the enemy's slice path. When it's your turn to attack, then waggle/swipe back and forth as much as possible. The general lack of health meters and the lack of swordplay inherent in their Ninja style means it's do-or-die gameplay.
3. There's a certain first-waggle or first-block you can do before combat begins, when done successfully you will have the advantage and attack first instead of blocking.
4. Avoid combat as much as possible get a better detection score, and to save the sword for more useful things like cutting locks or using it as a step-ladder where you see pinwheels stuck on walls. Most tools have secondary uses that help solve tough situations.