One of my most important work tools is a bingo wheel which I throw wooden balls in labelled with the projects I need to work on - I've found it absolutely impossible to run a schedule based on priority, they all need work all the time and thinking about which one is the most pressing is just wasting time. I spin out a project, set a timer and work on it for half an hour or an hour to take it forward, then I spin again until it's time to stop working. It sounds quite ridiculous but it beats every other system I've ever tried for productivity; you just have to make sure the right balls are in the cage, throw in more if a deadline is approaching or take some out if something gets less urgent. Statistically, as long as it all gets done on time, who cares what order it happened in?

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