Here's one I just learnt today....

Do NOT level up (or have full stamina or Raid Points) just before 12:00 UTC time when they do Maintenance (normally Tuesdays and Thursdays it seems).

If they are out for two hours like sometimes, that is 40 Stamina points lost (that you would not have regained) and 3 Raid Points lost (that you would not have regained).