Warning: If you plan on playing on Insanity difficulty, you must change it in the options now for the Achievement/Trophy to unlock. If you change it after leaving Earth, it will not count!
You should decide early on if you want to be a 'good' or 'bad' Shepard as this will dictate whether you give encouragement or firm answers to conversation choices. Positive choices are the top options, negative choices are the bottom ones.
Once the action kicks off, follow Anderson across the outside of the building, jump the gap, climb the ladder, slide over the vents and when he spots the Husks in the distance, ignore them and just slide to the ladder on your right. Melee all of the Husks that now appear, grab the Medi-Kit opposite the entrance for 100 XP. When you open the door, melee the Husk and then speak with the child in the vent. Reload your gun when picking up the ammo refills, then head outside again, run down to the trapped men and then take cover against the Cannibal Reapers.
Once they’re all dead, run across the platform and scan the Med-Kit on your right for XP and gel. Take cover behind the fallen items and you can now use Anderson’s Concussive Shot. You need to make sure that your target is highlighted, then bring up the options wheel and choose the power. This’ll deal decent damage to the Cannibals on this level.
Keep pushing forwards and pick up the M-8 Avenger Assault Rifle before accessing the radio. Now, when the Cannibals attack, you don’t have to fight them, the trigger for the ship to arrive is actually when you run out of ammo . So simply shoot your bullets into the ground from behind the cover on the far left and you’ll not run the risk of being killed ( very useful on the higher difficulties). Once your ammo is gone, you’ll escape the planet to start your first mission.