The misuse of the term "negative reinforcement" makes me sad.
I firmly stand behind natural responses combined with premeditated responses. In this way organic development takes place alongside manufactured development: to do this, you use both positive and negative reinforcement where needed or when it naturally takes place.
I can agree here. It is sort of along the lines of parenting 101, where a parent says "don't do this" and then follows it up with "do this other thing instead."
Use positive reinforcement to encourage or enforce new behaviors, such as completing combat before looting.Use negative reinforcement (Yes, we all know what I mean even if I am using the incorrect term) to encourage people to stop doing things that are destructive or harmful to the group as a whole.
So, to put it this way:
Positive first since who knows, the players might actually start doing what you want without any further action.
Negative second when Positive fails or the person simply does not respond to being asked to wait his turn in out of combat "turns."
One nice fix I found to one or two people doing everything is to go around the table starting at the first person to act in a clockwise or counter-clockwise direction if initiative has not been rolled. This more or less enforces the idea of allowing everyone to act in turn even if Billy and Bob are the ones who want to do everything. Of course, Billy and Bob could just leave a room while the rest of the party is still searching it and face the future encounters on their lonesome. I'm sure the other members will come to their aid if they hear the screams of either their party's men or the enemies.