To be really efficient, focus fully on the task at hand. I mean really give that task your full attention. That means no distractions, no multitasking. Studies have shown that short bursts of focus on one task, around 25 minutes, followed by a short break, are really effective in getting things done. Check out the Pomodoro Technique for more detail on how to use focus for your benefit.
What could you achieve if you gave your most pressing task your full focus?