When they kinda 'crouch' for a second, run out of range to avoid the fire. Their leap attack is pretty obvious and slow so you can dodge it after they jump even. I never had to figure out a specific tactic for them. It will hit him when he moves his shield out of the way to strike you and interrupt his attack. I did this with staves but I'm pretty sure it works with most weapons. How I dealt with the big shield guys when my character was weaker was stay far away from them so they would start charging at you, and when they get somewhat close, do a jump attack. I never got frustrated enough in Dark Souls to quit, but this game is really trying my patience because the combat just feels clunky and slow to me even though my character is set up to be as fast as possible. It just seems like my character is set on 50% speed compared to everything else and I have not had fun playing the game the last couple days because I can make no progress.
Other times the enemy will finish their attack I'll try to counter attack and my attack can not even finish before they start hitting me again. I have my character leveled to a 38, I am in green encumbrance, and my weapon swings a little faster than default but it is still so fucking slow that I can never hit a guy if they have a shield. I'm past the 3rd boss and the giant shield guys and weird tentacle things kill me all the time plus that one sword wielding guy (like the first boss) always heals constantly and my weapons are too slow to kill them. The bosses so far have been easier but the regular enemies in the level are really fucking me up. What is your trick? I have played all 3 Souls games and this game feels wayy harder or at least maybe a bit unfair compared to those games.