I need help on Halo 3. I had all of the skulls on except for Iron, Thunderstorm, and Blind. When on the Storm Mission on Legendary I can get through the first part easily, but when I get to the Wraith, AA Wraith, and alot of Ghosts I get stuck. What should I do?

I had like 5600 points and I lost them all cuz of them Ghosts.