Every decision is a hypothesis...
Decisions are about the future and while we can speculate about the future, we cannot know it because it hasn't happened yet. So each decision, in essence, says: I hypothesize that if I do this, then that will happen.
...so complete the hypothesis before you leave the room.
You need now to consider 2 things: what will the signs be that your hypothesis was right? What will the signs be that the hypothesis was wrong? Identifying these--at the same time as making the decision--will have an effect that psychologists call priming: just listing them will make you more alert to the signs should they appear. Otherwise, your biggest risk is that you will notice all the signs that confirm your hypothesis--but none of the ones that suggest you're on the wrong track. This also stops the hypothesis from becoming too personal or political: it's easier to revisit a choice when you have data suggesting your hypothesis isn't proven.
Take it one step at a time
Much of the time, we can't see the whole problem--only part of it. So ask yourself this simple question: how much of this problem do I have to solve today? Small decisions can move you to a place where you can see more--and decide more wisely. Don't be seduced by the false heroism of grand gestures.
Appoint devil's advocates
Charge someone in the room to articulate the reasons why you should not adopt a decision. But make sure this is not the same person each time; if they are, they'll get tuned out. But playing this role is an outstanding lesson in perspective-taking and most people learn, from doing it, how to become better critical thinkers. Appointing a devil's advocate has another advantage too: it signals that not only do you not mind argument, you welcome it. Most leaders say this but don't do it. (Historical footnote: Devil's advocates were originally introduced to challenge the saintliness of candidates for canonization. Unfortunately, the tradition has since been abandoned.)
Who are all the people to be impacted by your decision? Of those, who are the most vulnerable? The true test of a good decision isn't how it impacts the powerful but the powerless. So make sure you consider every stakeholder, every constituent. If it works for all of them, you're on firm ground. If it works for only a few, you can do better.
Revisit the original hypothesis
Whether the decision proved a good one (your hypothesis was proved) or not so good (your hypothesis remains unproven) you have learned something. Stop and think what that new knowledge is telling you. Then start again--with new information.