The New In Town trophy in Borderlands 2 is story-related and can't be missed.
You will unlock the trophy once you complete the steps below (taken from the Xbox 360 guide on TA by mast3r 0r0m1s):
*** Spoiler - click to reveal ***- Talk to Scooter.
- Take Eridium.
- Find two fuel cells in his garage.
- Put them in the hatches in middle of town.
- Go buy something from Crazy Earl.
- Put final fuel cell in place.
- Go to Rolands place.
- Talk to guy outside.
- Unlock door.
- Pick up message.
- Achievement unlocked.