Nothing here is comprehensive.

Paths: The path to Mastery needs to be Self Improvement - Power Source Acquisition - Channeling Power - [Feedback Loop Optional] - Attaining the Goal.

Power sources: Remember, more is better.
Name:
True Names (the essence of the whole)
Whole Selves (actually consuming the person's whole)
Curses

Mind:
Puzzle solving (power through victory)
Mental discipline (power through resistance)
Collective subconscious
Dreams
Philosophical power (power through understanding)
Psionic power
Secrets

Heart:
True love
Familial love
Burning hatred
Murderous envy
Heedless bravery
Impossible hope
Suicidal despair
Ancestral shame
Communal acceptance

Body:
Fleshly union
Physical sacrifice
Physical training

Soul:
Faith
Sorcery
Community
Bonding

Conflict:
Against the Gift
Gift vs. Gift
Intrapersonal
Interpersonal
Warfare
Contests

External natural:
Volcanic
Lightning
Wind
Gravity
Inertia
Friction
Crushing
Torrential downpour
Rushing rivers
Oceanic current
Tectonic force
Tidal force
Orbital
Nuclear force
Forging
Flame
Acidic
Tornadic
Hurricane
Movement

External supernatural:
Numen
Paradox
Magical
Religious
Curses
Gifts
Void
Miracles
Truth
Victory
Moments
Mysteries

Creating channels: One must be able to channel the power through the Gift and oneself. Every power source has a different likely method, but the main ideal is to create a Moment, to build a connection between the Gift and the power and oneself, that either fuses them or somehow harnesses them appropriately. A back-and-forth connection can work to amplify the power successfully, but a one way channel can work as well. Metaphors can be very powerful here, but literal connections can work as well.

Goal: One must know what one wishes the Gift to be Mastered to. The Gift can be Mastered to itself, simply making it more powerful in the user's hands, or it can be Mastered to oneself, making it bonded to the user's will. It can be Mastered to another Aspect, changing the Gift's nature, or it can be Mastered to an idea, ideal, or other concept, also changing the Gift's nature. The better defined this is, the better.