The right hand rests comfortably on the keys as shown, with your pinky resting on the first foot joint key. Because it is longer, your middle finger will be slightly more arched than the other fingers.
Thumbs should be slightly curved as much as possible (see illustration).
Wrong - straight thumbs:
Correct - curved thumbs:
The left hand thumb has two different keys it can play. Normally it will play the smaller key.
Your right hand wrist should be as straight as possible:
not bent:
Whatever you do, do not let the first joint of any finger bend backwards. This is a no-no for virtually every musical instrument. Keep the first joint of your fingers strong and slightly bent.