(These tips will assume the reader has a controller instead of a keyboard.)
If you’re uncertain about parrying at first, play on the Easy difficulty. On most difficulties, parrying is achieved through pressing the parry button while tilting the left stick towards the enemy you want to parry. On Easy, all you have to do is press the button. (This can be disabled if you’d prefer to play Easy difficulty without an assist.)
Remember to use the Skills you buy.
Here are summaries of all the skills you can unlock:
Aerial Parry: Allows Raiden to parry attacks while in midair.
Defensive Offense: Allows Raident to dodge. Incredibly useful for avoiding attacks you can’t parry. Dodging will not reset your combo counter.
Sky High: Allows Raiden to do an upward thrust with his weapon held in his foot. Used in speedruns to deal heavy damage to Senator Armstrong. 1)
Sweep Kick: Allows Raiden to perform a foot sweep maneuver.
Thunderstrike: Allows Raiden to channel air pressure into a shock wave.
Falling Lightning: Allows Raiden to kick foes from above.
Quick Draw: Allows Raiden to attack as soon as he draws his blade.
Lightning Strike: Allows Raiden to deliver a rapid series of attacks.
Stormbringer: Allows Raiden to use a tornado-like attack with his weapon held in his foot.
Marches Du Ciel: Used for Mistral’s L'Etranger. Allows Raiden to plant the weapon in the ground to perform a somersault jump before smashing foes from above.
Lumiere Du Ciel: Used for Mistral’s L'Etranger. Allows Raiden to extend the weapon forward in a special attack.
Cercle De L’ange: Used for Mistral’s L'Etranger. Allows Raiden to plant his weapon in the ground and use it as a pole to perform a spin attack.
Turbulence: Used for Sundowner’s Bloodlust. Allows Raiden to use a powerful downward strike.
Downburst: Used for Sundowner’s Bloodlust. Allows Raiden to use devastating spinning strike.
On a New Game speedrun, you will want to buy the ‘Defensive Offense’, ‘Sky High’, ‘Aerial Parry’, ‘Falling Lightning’, ‘Turbulence’, and ‘Downburst’ skills. 2)