I have the same problem, where I am mindful for a few days and then go back to my old bad habits.

I find that the way I start my day out makes a big difference. If I start to drift towards the fooling around online first thing, it could be 10 AM before I get around to doing anything useful. The longer I can resist temptation to do the bad habit stuff, the more likely I am to work on the things that are more important to me.