Do (for those heavily involved in church, especially if you are in the choir): decide carefully in advance which services you will attend, and which you won't, and stick to it. With 25th Dec being Monday this year, there were four services in 26 hours. I declared very firmly that I would not attend all four. I found a reasonable compromise was to go to the special ones, but to skip the regular Sunday ones in December.
Don't: do treat food all the time, especially all through Advent! My system can't cope with so much sugar.