Parry riposte, you don't need to keep guard up, just learn the timings. Learning these was horrible, had to unlearn everything Dark Souls taught me, you have to parry as they start their strong attack. Basically a second before the attack will actually hit you. if I went back to Dark Souls now, I'd be eaten alive.
Also don't walk, run or roll. Just use the sidestep/dodge thing for all your movement, back off and always make them come to you.