First, and as a general approach, I'd pick ONE "habit" and try to break it. Then I'd look at the next habit. This point is separate from how you actually do that.
They (who ever they are) have said that it takes about 21 days to create a new habit. What they mean is something like working out or what ever -- force yourself to do it for 21 days and that might be sufficient to then not have to "force" your self much to keep it up. My experience is that a habit can be broken in a similar way.
Also, I think the number of days is arbitrary and very individual. For example, I went through a period of time where I often had an urge to play a "quick game" of Spider Solitaire when I was supposed to be working. It turned out that after a week-long vacation without computer access I no longer was interested in the game at all.
Second, as far as the best techniques to break habits go, it will depend on you and your habits. But I can offer something that has worked for me. Often tangents would start when I came out of "flow" to answer email. The thought process was that I was out of "flow" anyway I might as well do something else before I try to get back into it. The result was that I often stayed out of "flow", and on the tangent, for a LONG time.
Long story short, I tried turning off my mail client for the day, or turning it on at scheduled times as often as was needed. For me morning, mid-day and end of work-day checks kept others from being upset about slow responses. For several of the other sites that became problematic I used the Firefox plug-in called LeechBlock. That plug-in allows you to define a fine-grained site blocking schedule (e.g., no ebay or cnn from 9 to 5). In a question I have posted I describe how I handle my daily web-reading now.
Keep in mind that you ought to work on ONE habit and stay at it for as long as you need to before going on to the next one. I give a lot of credence to the idea that willpower is a limited resource that needs to be used wisely and sparingly. See this article on [ Ego Depletion ] for more on this theory,