It's been said that time management is mostly about choosing what not to do. If you accept the fact you can't do it all, and learn to turn things down without guilt, you can free yourself to focus on the things you consider important.

John Dettenwanger has mastered these ideas. As senior vice president and CIO of Ahold USA, he is responsible for all of the information technology supporting seven hundred fifty grocery stores and more than a hundred thousand people. He points out, "In the retail business I'm in, and especially given the size of Ahold in the United States, the speed of change is mind boggling. If you can't figure out what's important and what's not, you'll quickly drown."

He goes on to say, "There's a stream of stuff coming at you. I don't believe you can manage it. The question is more one of how you can navigate through the flow - not how you alter it."

Dettenwanger explains a simple technique he uses: "Literally every morning, or at times when I feel I'm being washed away by the current, I make a list of the top three of four things I really need to stay focused on. Then I keep that list in front of me."

The CIO of Ahold USA also tries to look at what can be done later. "It's not always about what you can move up", he says. "It's also about what you can move out to a later date. You might think of this as just-in-time planning."

And some things you can completely throw out. "When deciding whether to do something, try to first be objective in analyzing what's the impact of doing nothing. Think carefully about that alternative before assuming something has to be done. If the impact is marginal on anything you have the opportunity to do, you can just throw it away. And don't carry any guilt around about what you don't do."

For people who have trouble turning things down, Dettenwanger has a few tips: "When I have to say no to somebody I try not to make it personal. I try to put the emphasis on what's behind their request and what's behind my refusal. Sometimes I'll tell people I like their point of view, but that's just not something we're going to do. Or I might say I like the quality of the work they've done, but I don't like what they're proposing."

"Other times I'll say that I could just decide we'll not do it, but I'd rather hear their arguments. I let them express their rationale and then I need to express mine. It just comes down to a business decision."

On email, Dettenwanger says, "Sometimes I think we've done ourselves a great disservice by inventing email. It's created the ability for people to throw so much irrelevant work at you. And here's a prime example of where you have to sift through things coming your way and decide whether it's really important, or if it's just informational — that is, not something I need to act on."

One of the things Dettenwanger encourages people who interact with him to do is to be more clear and concise in their requests to get time from him. When sending meeting invitations, this means having a title and an agenda. If you put a meeting invitation on somebody's calendar with no discernible purpose, it's very difficult for that person to evaluate whether or not that meeting is important.

"I really stress the need to be clear in communications about why you want my time", he says. "What will you do with it? It's not that I'm important. It's the other person's time also. As an organization we need to be weighing the benefits of individual commitments of time."

In fact, on the morning of our discussion on time management, Dettenwanger had scheduled an appointment with the CEO two hours later. This particular meeting provided a good example of the importance of being concise in communications.

He says, "People send me tons of information to prepare me for a meeting with the CEO. I have to spend time bringing down a twenty-five page presentation to four pages. The head of the company doesn't have time to go through a lot of extra information. I need to be clear in what I'm telling him. I don't want to waste his time."

Think about the individual you're trying to communicate with. Look at your meeting as an investment on the part of that other person. Think about how you can make it a profitable investment.

Recognising the importance of focusing on one thing at a time, Dettenwanger says, "When I get home, I shut off my anxiety devices: the BlackBerry and my laptop. I just create a wall. If something is really important, people will call me. They have my phone numbers. I try to put work aside. It will eat you up. How many people feel they have to look at the BlackBerry just because it's vibrating with a new message. I shut it off. I put it somewhere else. I don't want to look at."

"When I'm working on something, I try to clear everything else out. When I'm not at work, I try to leave work out, and just completely focus on something else. It's a way of removing the clutter from my mental space."

"There's a rather extreme exercise we try to do as a family at least once a year. We like to go out into the wilderness to go camping. When we do this, we really go out. We don't take radios or phones. We don't even take watches. We completely disconnect."

"We might go out to Colorado - to places where cell phones wouldn't work even if we took them. A couple of years ago we went off in the mountains and set up a camp in the wilderness for ten days."

Dettenwanger says, "You come back so mellow. It really helps you realise there's stuff going on around you that really doesn't matter. It helps you cast the unimportant things aside."

Spend some time figuring out what you don't need to do.

Pat Brans is author of Master The Moment: Fifty CEOs Teach you the Secrets of Time Management, and is visiting professor at the Grenoble Graduate School of Business