As much as possible, it’s best to focus on a single task at a time. With intention.
That means, instead of constantly switching around (the default mode for many of us), it’s best to pick one thing and set aside some time (10 minutes, half an hour, etc.) to focus on just that thing. If it’s important enough to take up your attention and time, it’s important enough to give it the space for complete focus.
Leo Babauta | Zen Habits