Involve other people

Dr John Michael, a philosopher at Warwick University, studies the social factors involved in making and keeping commitments.

He says that we are more likely to keep resolutions if we can see them as being somehow important to other people - that "other people's wellbeing is at stake" if we fail.

That might mean committing to attend a class with a friend. The effect could be even stronger if you have to pay in advance - once we feel someone has invested time and money in something, we are more likely to see through our commitments.

Dr Michael is currently testing the theory that we are more motivated to prevent loss to other people than to ourselves.

Early evidence from this work suggests that people may be more motivated to continue a boring or difficult task when somebody else has invested effort in it.

Specific cues

Reputation is also a powerful motivator. Making your resolutions public can help you to keep them since the fear that people will think worse of you if you don't see them through will add to your resolve.

"We don't want to get a reputation as unreliable, so publicly announcing our plans can be motivating. Betting can be still more motivating," says Prof Neil Levy at the University of Oxford.

Making detailed resolutions is important, he adds.

Saying, "I'll go to the gym on Tuesday afternoons and Saturday mornings" is more likely to be successful than simply saying "I'll go to the gym more", according to Prof Levy.

He also recommends tying your intentions to specific cues, a practice he calls "implementation intentions".

If you want to learn a language, you might first resolve to listen to a language-learning podcast on your commute each morning.

Then, to improve your chances of success further, you could make sure you stick a note to the steering wheel of your car each night to remind you to play it on your journey in the morning, for example.

You're not just making a intention but also setting out steps to implement it.

Making exceptions

He also warns of the potential for "decisions to become precedents".

"Implicitly we recognise that there are exceptions (I won't go to the gym if the house is on fire). But we can exploit this to our detriment by expanding the exceptional circumstances.

"My birthday may be a legitimate exception which comes once a year. But if I start recognising as exceptional things that occur more often - it's the last week of the month, better to start on the first; or it's too cold to get out of bed so early - then everything tends to become an exception," Prof Levy says.

Make them part of your longer-term plans

For Dr Anne Swinbourne, a behavioural psychologist at James Cook University, Australia, the best resolutions are the ones that achieve a chunk of a longer-term plan you have for yourself, rather than those that are vague and aspirational.

If you've never shown an interest in sport, resolving to become a brilliant athlete is unlikely to stick - resolving to save money because you've always dreamed of travelling the world before you turn 50 might be more successful.

And keeping them is all about planning, she says.

Work out what your triggers are, both to negative behaviour you want to discourage and positive behaviour you want to encourage - if you want to drink less, plan to meet friends for coffee not in a pub.

"People who rely on willpower mostly fail," according to Dr Swinbourne.

"To keep a resolution, you have to be boringly meticulous - you have to plan."