Simply complete all missions given from NPCs/Bounty-Board within the first area. Clap-trap quests also count towards this achievement. Here is a list of every mission in the Arid Badlands:
1. Leaving Fyrestone
2. Claptrap Rescue
3. Get the Flock out of Here
4. Blinding Nine-Toes
5. Nine-Toes: Meet T.K. Baha
6. Nine-Toes: T.K.'s Food
7. Got Grenades?
8. Nine-Toes: Take Him Down
9. Nine-Toes: Time to Collect
10. What Hit the Fan
11. Catch-A-Ride
12. T.K. has more Work
13. The Doctor is In
14. T.K.'s Life and Limb
15. Bone Head's Theft
16. By the Seeds of Your Pants
17. The Piss Wash Hurdle
18. Circle of Death: Round 1
19. Get a Little Blood on the Tires
20. Hidden Journal: The Arid Badlands
21. Shock Crystal Harvest
22. Sledge: Meet Shep
23. Sledge: the Mine Key
24. Fix'er Upper
25. Insult to Injury
26. Sledge: To the Safe House
27. Circle of Death: Meat and Greet
28. The Legend of Moe and Marley
29. Scavenger: Sniper Rifle
30: Return to Zed
31. Circle of Death: Round 2
32. Why are They Here?
33. Product Recall
34. Circle of Death: Final Round
35. Scavenger: Combat Rifle
36. Sledge: Battle for the Badlands
37. Find Bruce McClane
38. Braking Wind
39. Schemin' That Sabotage
40. Fresh off the Bus
41. Job Hunting
42. Skags at the Gate
43. Claptrap Rescue: Safe House
44. Claptrap Rescue: Lost Cave
Have fun