Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

Underdog (50 points): Take the lead in an Event on Xbox LIVE.
You've Become a Phenomenon (50 points): Win all 5 Events and hit a fame ranking of 1800.
You've Become a Legend (30 points): Win all 5 Events and hit a fame ranking of 1400.
Professional Photographer (50 points): Take 60 single photographs / all-in-ones and 20 environmental photographs.
Seasoned Veteran Photographer (30 points): Take 25 photographs of other riders on Xbox LIVE.
Rider of the Year (100 points): Beat Wolle, Annie, Travis, Tadashi, Nicolas and win 2 of the Events.
Amateur Photographer (20 points): Take 10 photographs of other riders on Xbox LIVE.
The Bandit (30 points): You "Owned" a Brand Battleground, stealing ownership from another rider on Xbox LIVE.
Turn of the Tide (50 points): "Own" a Brand Battleground and help your sponsor subsequently seize control of the mountain.
Method Event Winner (50 points): Win Highway to Hell in Alaska.
Asthetiker Event Winner (50 points): Win Wangle Tangle on Almirante Nieto.
Snowboard Magazine Event Winner (50 points): Win Shred Fest on Mt. Shuksan.
Absinthe Event Winner (50 points): Win Elements of Style on Diablerets.
Huck Magazine Event Winner (50 points): Win Air Party on Mt. Fuji.
Tour Guide (50 points): Earn a pilot license for each mountain.
South American Tourist (30 points): Find the Summit Cross and sign the guestbook on Almirante Nieto.
European Tourist (30 points): Find the Summit Cross and sign the guestbook on Diablerets.
Stomped It! (50 points): Score 500,000 points in a single run.
You're Sponsored! (20 points): Earn a sponsorship.
You're a Professional Rider (50 points): Hit a fame ranking of 186.
Nature Lover (10 points): Capture 10 photographs of nature.
Methodology (10 points): Complete all of Wolle Nyvelt's tutorials.

Additionally, there are three secret achievements:

The Call of the Wild (30 points): You found the crashed UFO and signed the guest book in Alaska.
The Cascades (30 points): You found the Summit Cross and signed the guestbook on Mt. Shuksan.
Into the Fire (30 points): You found the Peace Bell and signed the guestbook on Mt. Fuji.