I'm a student having a hard time having to study 6+ hours a day on the 8 hour free time I have, trying to enter the university I aim for (I'm Brazilian). When I started this regime, the hardest habit to drop was the internet, of course ;) My solution was radical. I gave myself a fixed (and limited) time frame where I could browse, check on email, update social network profiles, etc. I've been studying programming for a long time also, and there's a proper time frame for that too.

However I acknowledge it may be harder if you're in between: trying to control yourself but having it crucial to your job. As hard as t may be, I could only recommend my own strategy: trying to organize your time properly, and stick to it.