Only make promises I can keep.
We must be able to do what we say we can do. If we know we can't achieve it, we shouldn't promise it in the first place. Also, we shouldn't promise results if there's too many things out of our control (we can promise "I'll do my best to win the gold medal" but we can't really promise that we'll actually win it)

Only make promises for myself.
We can't control the will of others, so we also can't make promises for them. Either the other person is going to resent us for committing them; or if they fail to deliver, we'll be the one who looks bad. It's not a winning thing to do. It's better to get them to make their own promises if we need their help.

Don't make conflicting promises with another.
To be really true to the goal, we shouldn't make a promise to someone else that conflicts. One of them is sure to be deisappointed; maybe even both.

Follow through.
It's not about being able to make a promise that builds our character and our reputation. It's about us actually coming through on them. To become known as someone who follows through helps us as much as it helps them.

Follow up.
How will we ever really know if we "did good" unless we ask? Getting the feedback not only tells us whether we've succeeded or not, it helps to show we really, really care.

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Guru-cize it

Start small. Think of the little promises we make during the course of the day."I'll pick up bread on the way home" or "I'll call you this afternoon" and write them down. Have a little "promise book" in your pocket; like a "to do" list but only of the things that have been committed to someone else.

Then make sure to check them off.