So, like, how do you Ninja Gaiden? The Razor's Edge demo was the first time I've ever played a Ninja Gaiden game and I can't get anything done for the life of me. A simple crowd of regular enemies decimates me and I have no idea what to do? I want to unlock Kasumi ;___;
I'm not a great NG player so it's better that you wait for the answers of more expert players, but I can say that surely the first basic rule to keep in mind is
"the defence". You can't go too much forward if you don't think first of all to keep your guard on and dodge the adversaries to take distance by them or simply to look for a better position. Overall at high difficulties, you can't hope to win just attacking when you want, you have to look for the right moment and the right timing.
In general, defend, dodge and attack can be the most simple but effective strategy to use at basic levels of the game.
For the rest I suggest you to see some playtrough of the game on You Tube, you will learn various tricks and strategies to use, and this will improve surely your knowledge of the way to play in really short time (off course the practice is antoher matter).