For me, the biggest problem is the start of the (boring) activity. Once I'm already in it, I can work for hours -- just the first step.

So my solution is simple. I say to myself: "I'm not gonna work on that boring thing, I'll just have a look at it." This relieves the pressure and allows me to get started. Next thing is: "Ok, so I'll just do this one little thing." Three hours later: "Shit, it's done.".

Also it helped me to write down activities I want to stop, e.g. "No HN before 5pm; No news before 5pm".

And the last thing is to remove all possible distractions. Put your phone out of your visual field, block sites, etc.