Here is one thing that helps me:
Block out work time and allocate relaxation time for each day (relaxation does not mean sleep). You cannot work 100% of the time, but you need to be vigilant about not engaging in leisure activity during a work time block.
Intersperse designated play time in between work times, but do not let the two types of time periods overlap and become blurred. If you find an interesting website during working hours, bookmark it and come back to it during the next play time period.
Basically work during the work time, play during play time, and maintain consistent waking/sleeping patterns (try to go to bed on time).
Another thing I forgot to add was don't squander your prime time hours, whether it's by self-distraction or by others distracting you.
So for example if you get your best work done in the morning before noon, schedule all appointments and meetings in the afternoon. Minimize breaks during your prime hours, since you probably don't need as many. If you're an evening type of guy, then take care of events and social activities earlier in the day whenever possible.