Keep your promises. Espeically the small ones that are easy to let slip. And when you break or slip up on one, directly acknowledge it with them and apologize while trying to make amends. Even (especially, really), if they don't remember. Raising a child that keeps their word is 100% modelling, not lecture. You have to show them how to build those skills by demonstrating them daily, while reinforcing that with direct explanation of what you're doing or thinking in relevant contexts.
Simply put, don't hold them or yourself to a standard of perfection or pure honesty, expect accountability and integrity, even in failure or mistakes. It's just as important how we handle when we fail through our own mistakes as trying to avoid making them.