Check out this post by Tony Schwartz that talks about some of the things you can do to increase your productivity, including focusing on one thing at a time without interruption.
I have been trying to do the “one thing at a time” approach as much as I can with my work, and it has been working well. This is what made me decide to create the “Focus Light” feature in WatchMe. You can tell the app how focused you want to be, and it watches how often you’re switching tasks (via your timers) and gives you feedback on how “focused” you are. As long as I’m keeping my light green, I know I’m on track.