One thing that I would do is to never promise something that cannot be held. Especially with children.

How often, my son is asking me something, I answer it positively, but under the (not guaranteed) condition I can find the time. And then he often asked me to promise that I will do it soon. Unfortunately, I cannot promise something I am not sure I can respect, even if I would like to. So no... :)

As a result, when I promise something, he knows I would hold my words!