Gather as much information as you can
Facts, obviously, but also the 'softer stuff'. Who are the key stakeholders in the decision? Who will be affected by it most? Who can block it? How do these people feel about it? How can they be influenced? Getting this information out of them without giving away your intentions is an art you can work at mastering.
A decision is a process, not something that happens in a moment
Make a plan
A decision is a process, not something that happens in a moment. Information gathering is just a part of this. As you learn more about the world of the decision, options for action crystallise. A 'frontrunner' usually emerges — and if you are lucky, this will turn into the actual decision you make. The decision then needs to be implemented in a planned fashion.
It's easy to think that a quick decision is a good one, a sign of being 'decisive'. Great decision makers take the time they need to make great decisions, then implement them skilfully. Clearly, great decision makers don't dither, but that's a different matter...
You almost always have more time to make a decision than you think. (While some decisions are snap ones, where speed is of the essence, most are not.) Salespeople often try and inject urgency into situations: the savvy decision maker understands this and creates the space and time needed to get the decision right. Deals often get better once you start resisting this artificial urgency, too, as there may be pressure on the other person. Have your own timetable in mind and don't let people with other agendas push you off it.
Keep the big picture in mind
Ask yourself what the decision is in service of. How does it fit into wider contexts such as personal and institutional values?
Have clear, 'must have' outcomes
Negotiators are taught to distinguish between 'must have' outcomes and 'would like to have' ones. Know what your 'must haves' are, and don't compromise them. A decision can be seen as a kind of negotiation with fate. Use negotiating skills to make it a successful one.
Give yourself 'wiggle room'
Even the most careful decision is imperfect: you can never get all the information you need and events can keep changing. A good decision leaves space to adapt to changing circumstances while it is being implemented. 'Decisiveness' — often seen as closing options irrevocably and quickly — is rarely the wisest course.
Have an escape route
Sometimes even the best-made plans don't work out. The world changes fast, and decisions have to be abandoned. Deciding to do this is, of course, another decision, with its own timeline.
Follow your intuition
Cerebral activities are essential aspects of decision making — but at its deepest core, it is an emotional process. The best-made decisions are made with head, heart and gut in agreement. If your head argues yes, but your gut feeling says no, take time out to find out why.
Decision making is an art you can enjoy practising and getting more skilled at. You will make mistakes: so learn from them and move on. More important, you will make ever better decisions.