Here's a tip. If you have the knight shield, upgrade your stamina or shield and try to take out Ornstein first and afterwards Smough's movements are very easy to predict. You can block all of his attacks without taking damage though watch your stamina for if you don't you can easily get killed. Stay behind the pillars as well being Smough's charge attack cant go past them. Now if you're aiming to kill Ornstein last kill Smough the same way though it may make things difficult. When you fight mega Ornstein i would recommend range over close range like for Smough. Other wise it all depends on the other equipment you have. That knight shield can really help. It blocks EVERYTHING except magic which you will never really see at all when it comes to bosses.