When it comes down to it, the secret of productivity is to just do it. In our line of work, it's not as simple as you're either chopping a tree down or you're not. So it's easy to get distracted on tangential or unrelated tasks and trains of thought. If I didn't know people personally who somehow manage to avoid this trap most of the time, I'd think it was impossible. For the rest of us, I present a nifty trick.
Grab two condiment bowls, shot glasses, rolls of tape, whatever. Now grab some glass "stones", some pebbles, some M&Ms, whatever. The former are buckets. The latter are tokens. Put all the tokens into bucket A.
Now for every hour you work (really), move a token from bucket A to bucket B. Do this every day for a week and keep a tally. This will show you how much time you are working and how much time you are squandering. It will be depressing. Don't let your boss see.
Now decide how much time you will permit yourself to squander. You might feel that should be 0, or maybe you feel you deserve an hour a day. No matter what you feel it should be, make a realistic goal at this point. It's just like physical excercise you know. So figure out the ratio between work time and play time. 4:1 makes the math convenient, so let's take that ratio. Now, for every hour you work you bring a token from A to B. It represents 4 quarter hours in bucket A, but only 1 quarter hour in bucket B. That is, you get to play 15 minutes for every token you have in B. Think of it as a bank account. If you don't got no tokens in the play bucket, you work. If you do, you might keep working because you're in the zone. But you might play, because you have the tokens to do so. So play, and play guilt free. The guilt-free recreation is as important as anything here. If you can't bring yourself to give yourself permission to play at work, then split it up between stuff you hate and stuff you enjoy. You do enjoy some aspect of your work, no?
This is just a slightly-modified token bucket scheme, like that used in network shaping (e.g. Quality of Service). When I first came up with it, I was inspired by "token economics" which was suggested for potty training. When I had the system going for a day or two, and was working on a QoS presentation, it dawned on me that what I had here was a token bucket. That makes it all the more cool.
What good is it? I think it's an effective tool for a couple of reasons: it's simple, unobtrusive, and authoritative. It keeps you accountable, both to it and to yourself, and to anyone who looks on that knows what it means. It doesn't nag you, nor is it susceptible to your rationalizations. It's easy to reset or set aside when it doesn't apply (when a deadline looms and you don't have time to play at all). The only habit you need to get into is checking your account before playing. But if you fail to remember, you can always adjust the totals retroactively, in which case although you may have overdrawn you will still see the state of affairs, and have an opportunity for introspection.
Now if you'll excuse me, my play bucket just ran out.