Practice, mostly.
There’s also a few entities who might be useful:
- Asmodai (Goetic demon/djinn[?]): to develop a skill to a level previously thought unattainable
- Nenael (Shem angel): improve skills in any area
- Yeyizel (Shem angel): increase psychic abilities
- Ublisi (Angel of “omnipotence”): “hear” thoughts
- Raziel (Archangel): unlock magickal ability
- Vine (Goetic demon): improve magickal strength
- Furcas (Goetic demon): improve psychic ability
- Seere (Goetic demon): achieve more in a shorter amount of time