7 rules for making changes that last

FORTUNE — Most offices, maybe even yours, have some equivalent to the cookies in Goldman Sachs’ (GS) conference rooms. Caroline Arnold, a managing director at the firm, used to eat several snacks every time she met with colleagues or clients.

Each cookie was “probably 350 calories,” she writes in a new book called Small Move, Big Change: Using Microresolutions to Transform Your Life Permanently, and “produced a sugar high so powerful that it could outlast the longest meeting.”

Unfortunately, the sweet treats also played havoc with her resolve to lose a few pounds. So she made a small change, or what her book’s subtitle calls a microresolution: No more conference room cookies. The key, she writes, was that “I didn’t resolve never to eat a cookie again, or never to eat food in a conference room again … Because my resolution was reasonable and specific, success was easy to measure” — and to repeat until it became second nature to pass the cookie plate along without taking any, which eventually led her to cut calories elsewhere as well.

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In explaining how small changes produce big results, Arnold quotes Aristotle: “We are what we repeatedly do.” Most of what any of us do on any given day is dictated by habit, or what Arnold calls “autopilot.” The key to changing entrenched behaviors, by her lights, is to alter our autopilot a little bit at a time, using microresolutions. These seven steps, from her book, explain how:

1. Microresolutions should be easy. Most resolutions don’t stick, Arnold says, because they’re too big and vague. Instead, she says, start with “a discrete change in behavior that will make a difference.” Rather than resolving to get in better shape, for example, decide something “limited [and] achievable”, such as walking to work one day a week. Once you’ve been doing just that one thing for a while, she writes, it will be easier to make other fitness decisions.

2. A microresolution is an explicit and measurable action. If, for instance, you resolve to react less defensively to not-so-hot feedback at work, she writes, “you’ll need to think about the specific circumstances under which you become defensive, the form your defensiveness takes, and what explicit message you can send yourself” to stop it. The more specific you can make your resolution, in other words, the more effective it will be: “Flexible or fuzzy resolutions, escape clauses, and loopholes”, she writes, will just stress you out and make it easy to give up.

3. A microresolution pays off up front. Human nature being what it is, we crave instant gratification and have trouble caring much about hypothetical rewards that are somewhere in the foggy future. “If your resolution delivers only after months of effort and you quit ahead of time, you end up empty-handed,” Arnold notes. “Getting ‘paid’ up front” — that is, every time you succeed at one task you’ve set yourself — will “leave you eager to nail your next microresolution and its reward.”

4. A microresolution is personal. Forget about resolutions that reflect what someone else thinks you should do. “To be effective, a microresolution must be designed for you, by you, based on observations of your own habits, attitudes, and situations,” Arnold writes. For example, lots of people resolve to get to work on time, but “solving late arrival will vary by individual.” One approach: Examine the entire series of actions you take before you leave home, she suggests, and start doing one or two of the most time-consuming among them the night before.

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5. Frame your microresolution in a positive way. “Most of us would rather follow a positive directive than a negative one,” Arnold notes. “A resolution not to snack is pretty dismal.” By contrast, “the microresolution message ‘I enjoy dinner so much more when I’m hungry’ steers the tempted snacker toward a more gratifying goal.” Whatever your resolution may be, she writes, put it in terms that will motivate you, not bring you down or make you feel deprived.

6. A microresolution fires on cue. Since much of our behavior happens in response to cues in our environment, Arnold writes that the key to changing anything is recognizing those cues and making the most of them. To make a resolution you’re certain you can keep, focus your effort on one cue at a time, she suggests — reminding yourself as soon as you set foot in the conference room, for example, that you’re not eating any cookies there.

7. Make just one or two microresolutions for now. Citing recent brain research showing that attention and self-control are both limited resources, Arnold counsels against trying “to change too much too fast. Limiting your resolutions ensures that you have the attention and endurance to stick with a behavioral shift until it becomes autopilot … As soon as one of your resolutions is solid and isn’t taxing to maintain, you can start working on a new one.”

By this timetable, anything you started on Jan. 1 has some time left to go before it’s “neurologically embedded,” Arnold writes: A microresolution “will take around four weeks before it begins to feel less awkward, and six to eight weeks before it begins to feel natural.” Hang in there.

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