For those having any troubles staying alive in these Primal Trials here are some guides to help you along:
These are farmed often for the Pony Mount
The Howling Eye (Extreme)
The Navel (Extreme)
The Bowl of Embers (Extreme)
The Whorleater (Extreme)
The Striking Tree (Extreme)
Akh Afah Amphitheatre (Extreme)

These are farmed for vanity pieces
Thornmarch (Extreme)
Urth's Fount