It amazes me that this has to be said, but this should be your cardinal rule at work:
Do what you say you’re going to do, by when you say you’re going to do it, or update people accordingly.
Every single time. No matter how small.
Why? Because your word should mean something. Because your credibility is at stake. Those things matter.
This behavior is so uncommon that if you do it 100% consistently, you’ll develop an awesome reputation for being reliable and keeping your word, no matter how tiny the issue at hand. People notice this stuff, and they remember.