With very few exceptions there are only two ways to regain mana and theurgy: Rest and meditation. Both of which require no other activity except relaxing and allowing one's spirit, chi or whatever energy collecting methodology that is believed by the wizard or priest in question to take place. This includes races such as elves and deadeyes who require reduced amounts of sleep or no sleep at all. They must still meditate or otherwise concentrate on re-accumulating mystical energies in order for their personal battery to recharge and be ready to execute spells. Below are restrictions on recovering theurgy and mana.
Mana is generally recovered with an 8 hour rest or meditation period. Such periods are broken down as follows:
1 hour settling/focus period is required before ANY mana or theurgy begins to recharge (i.e. - if a wizard is awoken with 1 hour 30 minutes of sleep they will regain NO mana)
For each full hour rested, a priest or wizard regains one seventh of their total mana or theurgy pool (just divide the total by 7 and round down)
For specialist mages, mana recovers with the normal 60% general 40% specialist pool break down
Keep in mind there are special situations that can change this which the DM can and will explain to you in given situations