Instructions
Complete five of the missions given to you by the NPC Bounty Board in the Arid Badlands to unlock the "Paid in Fyrestone" achievement, which is worth five points. You must complete at least five such missions to advance in the game, so you should get it with ease.
Earn the "Made in Fyrestone" 15-point achievement by finishing all 44 missions in the Arid Badlands. This includes the "clap-trap" quests. Many of these missions are optional in the game.
Finish five missions in Rust Commons given to you by the NPC Bounty Board to get the 10-point "Paid in New Haven" achievement. This is another accomplishment you must earn to advance in the game.
Complete all 59 missions in Rust Commons to unlock the "Made in New Haven" achievement, which is worth 20 points. This also includes the "clap-trap" quests.
Work with a friend and complete 15 missions in the cooperative mode. This will unlock the 30-point achievement called "There's No 'I' In 'Team'." You can play cooperatively over Xbox Live or on splitscreen or system link to earn this achievement.
Defeat several bosses in the game to get some more achievements. You will earn 10 points for beating Sledge, 20 for finishing off Krom, 30 for killing Flynt, 40 for beating the Rakk Hive and 50 for eliminating the final boss, the Vault Boss.
Beat these same bosses in a cooperative game with a friend to get the "United We Stand" achievement that is valued at 35 points. The bosses will be harder with two players, but this is mitigated by the presence of the second player.