做主 To be the master. To take charge and decide. The Handian dictionary gives the example 你大胆干吧，一切由我做主, “Go ahead boldly. I will decide everything.”
拿主意 To take hold of an idea. To make the decision on a matter.
定夺 To fix and to take. To decide whether a thing will be done, or which option will be chosen.
定调子 To set the key. Originally to fix the pitch of a piece of music. Figuratively, to set the basic direction before a piece of work begins.
当家 To head the house. To manage the household.