First step is to notice I am procrastinating, next I decide what the minimum time is that I would be happy to commit to get started on the task, then I set my timer. Sometimes it is only 5 minutes, other times it is 20 minutes or half an hour. Whatever the amount of time I have to be happy to commit to doing that, and then I give myself permission to make a choice to continue or stop when the timer goes off.
If I do choose to stop when the timer goes off, I know I am a step further ahead than I was when I started and that I had kept my word to myself about doing what I said I was going to. However, I have noticed that invariably once I get started I am happy to continue on until I have completed the task or it comes to a natural stopping point.
I have found this to be a simple and easy to use technique when procrastination strikes and so have my clients.