This achievement requires you to get 100% ratings for all 6 reports in both normal and extra mode. This means that you must successfully hit every hidden command in each report - see the "Secret Explorer" achievement for more information on this.
Perhaps the most useful thing to remember when going for this achievement is that most levels have checkpoints; if you've made a perfect run up to a checkpoint, you can use the "Continue from Midway" option on the pause menu to reset yourself to the last checkpoint if you mess something up. As such, it's good to know if you've hit everything possible up to each checkpoint. Here is a list of the percentages you should be at for each one:
End of Part 1 - 73.5% (loading screen before boss fight with singing robots)
End of Part 1 - 49.5% (loading screen before guitar battle with Pudding/Padding)
End of Part 2 - 79.5% (loading screen before boss battle with giant plant)
End of Part 1 - 46.4% (loading screen before entering the station)
End of Part 2 - 78.0% (loading screen before reaching the core)
End of Part 3 - 100% (loading screen before escaping the station)
End of Part 1 - 56.0% (loading screen before the band battle)
End of Part 1 - 76.0% ("please wait for a moment.." screen)
During report 6, you should be at 199% before the credits begin -- be sure not to miss the very last phrase after the credits end!