Drink plenty of water and avoid high sugary, fatty foods which may create a sugar boost but also creates a sapping lull.
Avoid alcohol during the week.
Exercise even when disinclined for an energy boost and to work off frustrations, so you don't take them home with you.
Do not take work with you on holiday.
Heads should set a good example: leave work on time so staff feel comfortable leaving on time.
Ask why you are doing something and whether it is worth the effort.
Avoid pointless meetings with little outcome.
Use spare time effectively - read on the train.
Smile - it tells people things are going well and creates good feeling.