There are 8 different playlists you can choose from to earn this achievement.
-Easy Campaign
10 missions - All 10 campaign missions, easy difficulty, no skulls
-Normal Campaign
10 missions - All 10 campaign missions, normal difficulty, no skulls
-Heroic Campaign
10 missions - All 10 campaign missions, heroic difficulty, no skulls
-Legendary Campaign
10 missions - All 10 campaign missions, legendary difficulty, no skulls
-LASO Campaign
10 missions - All 10 campaign missions, legendary difficulty, 13 skulls on
-The Covenant Threat
3 missions - 3 campaign missions (Dawn, Requiem and Composer), normal difficulty, no skulls
-Canyon Combat
3 missions - 3 campaign missions (Forerunner, Reclaimer and Composer), normal difficulty, no skulls
-Tight Corridors
3 missions - 3 campaign missions (Dawn, Shutdown and Midnight), normal difficulty, no skulls
Just complete any one of these playlists and the achievement will pop afterward. Obviously, the easiest/quickest ones will be the playlists with the 3 missions each.