I screwed up. One tiny mistake. Suddenly I arrows were raining upon me and that knight suddenly shows up kills me. I'll go back there. And I killed every enemy in Anor Londo with my Lightning Spear. It worked fine against them. I know Ornstein and Smough have lightning resistance. Also, should I get that Lightning Stoneplate(?) ring from that guy in Sen's Fortress? Does it work well against O&S? I would have to grind a bit to get the souls for it.
No don't bother, all those rings that raise defense are not worth it. They seriously need to be buffed in Dark Souls II, I never used them.
Keep your equip weight below 25% so you can dodge fast in the fight. Kill Ornstein first and Smough later, that's the easy way to killing them. Super Ornstein is hard to handle, Super Smough remains mostly unchanged; he only gets lightning damage on his attacks.
After you kill Ornstein, equip the Red Tear Stone ring and get your health below 30% to activate its ability. Then just get Smough to repeat the hammer charge move while a pillar is between you and him, you'll be able to snipe him that way with a bow or a crossbow. Easy kill.