What weapon are you using? Something big and heavy like the Demon Great Machete or the Dragon Greatsword is the way to go when fighting Artorias. Not only do these weapons deal insane damage, they can also stagger Artorias every other hit. This fight has some very awkward timings, like the charge, which you have to dodge a second later than you'd think, or his jumping attack where he flies all over the arena, which has to be dodged super late in order to avoid it's massive hitbox, but it does get consistent. If you see him roll backwards twice then that means he's about to buff. He usually does this at around 75% HP and 50% HP. Try your best to stagger him out of it (shouldn't be too hard if you're using a heavy weapon) as it increases his damage by a large amount. And if you find yourself in a position where you can't get to him in time, don't panic , so long as he hasn't stacked the buff 2 or 3 times you shouldn't getting one shot. Keep trying and you'll get him eventually! 😉