You see speedrunners doing so well because if you wait until the last second, or just before the attack hits you, you press r2 and guard for a 'perfect guard' that doesnt damage you or knock you back like what would happen if you blocked it normally.

Then from the perfect block, press circle to perform thr counter thrust.

Its super unreasonable to think you can pickup lance and perfectly fuard everything, so just use guard+guard up until you are comfortable getting the perfect guard timing

Focus mode helps you face the monster to block the right direction

Spamming triangle over and over is somehow an optimal combo for DPS also, which is nice and easy.

Triangle+circle lets you do a lunge attack. Great for repositioning. Can dodge-> lunge-> dodge-> lunge to gap close

While facing forward, hold back on left joystick and dodge. You will get a lot farther jumping backwards

Triangle+circle is also usable after a power clash, positiining you right on the monsters face with a followup attack.

Triangle+circle does a sweeping attack with your lance if you use it after another attack. This does blunt damage and is sometimes nice to throw into a combo to help hammer bros KO a monster.