I've always had a problem keeping on target, either work or fun stuff. I've bounced around for years not really being able to put all my energies behind a task. The energy certainly gets used up, just on a variety of subjects. The first step that made a landslide of difference was using GTD methods. In conjunction with OmniFocus I've got a pretty good task management system that seems to serve me well. There's a blog post coming up discussing combining Omnifocus, Evernote & Basecamp to run life.
However, even with all my tasks lined up, sorted and available to me in exactly the way I need them, the actual doing of the work is still hard.
The pomodoro technique is simple enough to start doing right away and has, so far, yielded real results. The core of the technique is not much more than dividing your work into discrete chunks, or Pomodoros, setting a visible timer to monitor those chunks and taking regular brain breaks between them.
The full system is available online, for free in it's entirety although you can also buy an ebook version through the Apple store / Amazon etc. if you'd like.
Focus, focus, focus. I'm 15 minutes into a 25 minute Pomodoro and the blog post I have been putting off writing for a few days is done. EDIT now I'm drafting the post to check for typos and errors. Several corrected and I've got 4 minutes left. Enough to publicise the post.
I also just picked up some noise cancelling headphones that I'm hoping will help me filter out some audible distractions. I'm currently working with Friday on some work for one of the (very) large high street banks and although the office is great, it's very noisy and full of distractions.