(Reuters) – Have you already begun to fret over keeping that looming New Year’s resolution to shape up in the coming months?

Experts say while wishing will not make it so, visualizing your trimmer, fitter self can help to set you on the right path.

“Visualize your success,” advises fitness and wellness instructor Shirley Archer. “Imagine a perfect day where you are at fitness level that you want. How would you look and feel and what would you be able to do easily if you enjoyed your ideal fitness?”

Then, said Archer, the author of “Fitness 9 to 5,” get to work on specific goals.

“The typical mistake is being too vague and too large,” she said. “Instead of ‘I want to lose weight,’ say, ‘I will walk 10 minutes Monday through Friday.’ And don’t make those goals harder until you’ve achieved the easier ones.”

Big goals are fine, Archer believes, as long as you break them down, and learn from, and forgive, your inevitable backslides.

“Ask yourself why you did that but be emotionally neutral,” said Archer. “Get rid of that self-critic.”

She calls it training from the inside out, and admits it’s easier said than done.

“Studies show it typically takes about eight weeks to make a new habit stick,” she said. “So you have to work hard to change that mindset.”

January is the busiest month for new and returning clients at Equinox, the national chain of fitness centers, said Geralyn Coopersmith, who oversees the education of the training staff.

“It’s the same conversation: I need to lose some weight and I need to tone up,” she said. “We encourage them to project themselves a year from now: what would the transformation look like?”

Then, she says, she reminds them that Rome wasn’t built in a day.

“Coming in January third with guns blazing is not a good strategy. Slow and steady wins in fitness,” she said. “It’s not as sexy as ‘get into shape in 30 days’, but you didn’t get out of shape in 30 days.”

Instead, Coopersmith favors a customized approach.

“Fitness is not one-size-fits-all,” she said, “We want people to have an assessment even if they aren’t seeing a trainer regularly.”

She said clients left entirely to their own devices can make ineffective choices.

“It is human nature for people to gravitate to things they’re most efficient at, what they need the least,” she said. “Sometimes you have to go against the grain.”

Kevin Burns, spokesperson for the American Council on Exercise, urges swapping those grandiose dreams of enormous changes for two or three smart, specific and measurable goals.

Then write them down.

“Instead of saying ‘I’ll exercise every single day in 2012,’ set a schedule, set a time line, and be flexible but specific,” said Burns, a Minnesota-based fitness trainer for over 20 years. “A New Year’s resolution is a marathon, not a sprint.”

He also suggests looking back at your resolutions for the passing year, at what worked, what didn’t, and why.

“If it failed last year it will likely fail again,” he said. “Why start another year with failed resolutions?”

Whatever your path to fitness, Coopersmith said, realize that it’s going to take a little time.

“The difference between success and failure is keeping your promise to yourself,” she said, “and making a promise you can keep.”