Work on one thing at a time. Eliminate distractions. Avoid interruptions.
Multi-tasking is a myth. You cannot do it. When you attempt to “multi-task”, you are in fact switching rapidly between tasks. Switch-tasking requires interrupting what you’re currently working on to work on something else [Nass]. Interrupted, your brain takes twenty minutes to reboot [Gallagher, p. 154]. This makes you not only inefficient but confused. Worse, heavy multi-taskers actually get worse at juggling tasks and suffer from memory loss and diminished concentration [Nass].
(Note: It is okay to “walk and chew gum at the same time”, for these activities require different parts of the brain. You get the idea.)
References and further information:
Winifred Gallagher. 2009. Rapt: Attention and the Focused Life. Penguin
Herman Miller. 2007. The Siren Song of Multitasking
Clifford Nass. Multi-Tasking is Bad for Your Brain. GigaOm
Joshua S. Rubinstein, David E. Meyer, and Jeffrey E. Evans. 2001. Executive Control of Cognitive Processes in Task Switching. JEP
Sue Shellenbarger. 2003-02-27. New Studies Show Pitfalls Of Doing Too Much at Once. WSJ