Balance cooperation and competition
The players' decision to cooperate or to compete can lead to different strategies. Players could form teams in order to pursue a common goal or a common strategy. Team forming and cooperation could be fine-balanced through a system of rewards (or penalties).
A decision on if and for how long a cooperation lasts could be a one-off decision or it could be continuously assessed. Teams or players could enter a strategic temporary cooperation in order to eliminate an opponent and revert to competition afterwards.
Player decisions on whether to compete or to cooperate are can be accompanied by awarding different roles to players.
Example
Players with different roles often possess different game tools or game abilities. They might be tempted to cooperate in order to combine their abilities. They might choose to do so, for example, in order to reveal the position of a third player. In balance, this move could expose both of them to a danger or lead to a penalty.
Games that employ a bluffing pattern place the players in front of the dilemma of whether to trust a co-player and cooperate or to distrust and compete. Invisible City: Rebels Vs. Spies is such a game.