My opponent is the first player and he takes a player action that resolves.
The question is: who is the next player who can take an action? Me or him?
The FAQ 3.1 (page 14) states "When the game flow arrives at a player action segment, the first player is always allowed to take the first action. After the first action has been fully resolved, the opportunity to take another action goes to the player to the left, and so on (continuing in clockwise order)."
To give an example: if my opponent plays 'Dragon Lore' on his maester during the marshalling phase, can I kneel my 'Maester Aemon' (with 'Tin Link' and 'Valyrian Steel Link') to discard 'Dragon Lore' or am I forced to watch while he plays 'Balerion' at no cost?