On p. 103 of the main Sorcerer rulebook, step three in the order of Combat reads:

Everyone who's doing something proactive (not just defending) rolls at once. The order of the highest values rolled, from highest to lowest, determines the order of actions.

Clarification: In actual play, everyone rolls at the same time, even those choosing Full Defense. This establishes order of action and 'who's ready when'.

Note: Your roll for initiative is the same roll you use to determine success of your action when it's your turn. If you're initiative roll sucks, chances are very good you'll be aborting your action to defend.

Demons perform actions and make rolls just like other characters. Instructing a demon is a full action, so if your demon is faster than you are it will probably be moving on its own before you have a chance to tell it what you want it to do. (Or, if it's irritated with you, maybe it won't be moving until you tell it.)

Either way can be an advantage or a problem.

Holding Actions (Ron Edwards)

The initiative point is FIXED in Sorcerer. Announcement is announcement and resolution is resolution. Admissible changes to your choices during resolution are only for aborting to defensive rolls. No saved actions, and not 'holding action until after 'x' happens.' Your moment of player control comes during the Announcement/Free-n-Clear stage of combat, where everyone's deciding what they're going to do. Once the system goes into action, that's it. [1]

See also: Announcement Phase