Discipline is -at least in my opinion- the key to changing behaviours and increasing productivity. Pomodoro, GTD as well as other techniques are methods that need discipline in order to consistently use them and increase your productivity.
One simple tip to increase productivity is to award yourself after finishing a task instead of awarding your self before executing the task. Again, this requires discipline. This also holds when you want to change a behaviour. Changing behaviours requires you to force yourself to use this new behaviour for 21 to 30 day (depending on how you choose to belief) before it becomes a real behaviour. Once again, disciple!
How to improve your discipline behaviour without having discipline? (Not enough discipline)