If it plays the same that the original Prince of Persia (by Jordan Mechner) did, you have five buttons (the exact keys are probably different on an XBox):
- action (Shift)
Now, when fighting, Up was for blocking, Action for attack, and Down for sheathing the sword.
While fighting, you could also move closer or further away with Right and Left. Note that when moving close enough, you could switch sides with the enemy; enemy steps back when he is hit, you step back when you are hit. This could be useful e.g. for throwing an enemy into a hole, same height damage rules apply (one storey - no damage, two storeys - one life, higher or spikes - death).
As for fighting tactics, each enemy type (color-coded etc.) fights differently, and I don't recall the tactics any more - note however that each enemy of a certain type fights the same way. You may need to get closer to attack, or lure the enemy away, etc.
By the way: you can't kill everyone that you meet with a sword; be creative.