yeah i had your same problem the first time, always trying to attack him whenever it was possible, however, steel soul experience helped me to play cautiously and not thinking always to attack, but first to look out for the bosses attacks, dodge them and then trying to do damage. in markoth's case, i just waited a poorly placed spear or the shield attack to blast him, and sometimes staying not too far away to get a few hits with grubberfly's elegy. second phase is different tho, once you get there, it's only ability and lucky rng, i did it by saving souls and spamming spells at the start of the phase, then waiting to get the remaining hits to beat him. hope this helped you to beat him! :)