Multitasking--doing more than one thing at a time--rarely works. I'm not talking about walking and chewing gum at the same time. Those two activities use entirely separate parts of the brain.

The various sections of the brain--each with its own function--operate serially, not in parallel. That is, if you are accessing the frontal lobes to process visual information you cannot simultaneously access them to process auditory information. This is why you can't read a book and carry on a meaningful conversation at the same time.

The brain "sort of" multitasks, because the information coming to it is often below its bandwidth threshold. For example, if your brain can process 100 spoken words per minute and you are listening to 60 spoken words per minute, you have some leftover bandwidth. During the gaps between words, you can process other information. This is why we are able to carry on a light conversation while driving a car in fairly light traffic. But if either the conversation or the traffic ramps up, the driver will be unable to do one (or both) of the tasks properly.

Another problem with multitasking is there are transactional costs. That is, changing gears takes mental energy. The actual switching between tasks consumes some of that bandwidth and consequently takes up time.

If task X takes 10 minutes and task Y takes 5 minutes, you will use 15 minutes doing them separately. When multi-tasking, you can usually expect to take considerably longer--perhaps 20 minutes. Part of the extra time is due to the switching costs, part is due to the inefficiency caused by lack of attention, and part is due to having to repeat portions of the task.

So, to make the most of your time, avoid buying into multitasking myth. Instead, focus on the task at hand. To keep your focus sharp, break your tasks up into blocks that fit your attention span. If you are a television addict, you will have to keep these blocks small. If you are, say, a classically trained musician, try large blocks and see if you are maintaining your focused edge.

Here's an example of how this works. Instead of trying to balance my checkbook while planning a trip with someone over the phone, I might work on the checkbook until it's half done. Then, I'd call the other person and set some trip parameters--what we want to do, when we are leaving, when we are coming back. We'd agree to talk again the next day after each of us does some specific research. Then I'd finish the checkbook project and do my research (let's say I'm supposed to find the hotels and two places of interest).