After the big Firefight, when you finally clean out the room, you have to jump into a big Mac Cannon and take out the Mothership. Jump in to start it, then jump out and hide behind a Dropshield or Armor Lock. It helps but not essential, otherwise you have to memorize the pattern of lots of Banshees and Dropships which can be a pain. Then when you are told shoot the red middle core, jump back in and shoot, game over! Will help a lot on Solo Legendary.
Easy Credits
Just found another way to get easy credits while you are gone away with no fear of a banhammer! Go into Forge Mode into Forge world let your Spartan or Elite just stand there. Go away for few hours or go to bed and you will get almost 1,000 credits per hour. Make sure it's a plug-in controller.
Just to let people know, Bungie have a credits limit which is supposed to be 27,000 per day or max of 210,000 per week. Some have got the warning, others have gone well over with no warning. So get the easy Cr now!
Fastest way to rank up online is also this method above, or you can choose the Grunt Apocalypse Gametype to boost headshots, multi-kills and get the "Lemme Upgrade Ya" achievement very quick. Make sure you play onilne and you will get anything between 1000/2000 credits per game in about 10 mins. Much faster than multiplayer. Rumour is Bungie are going to patch this with lower credits, so make the most of it now!
Easy Lt Colonel Glitch
See video below. Credit goes to thestickman72 for the video. Submitted by Wannabe Actuary and IRELAND No.1
Glitches That Unlock Achievements 