It's that time of year again. We spend it eating and drinking far too much and falling down far too frequently. And then we head into the new year full of good intentions about getting fit and healthy again. Well, that's my routine any way.

Lots of us make new year's resolutions but few of us see them through. So what's the trick? How do you change the habit of a lifetime? Is there a technique you can use that doesn't involve wiring up your jaw? You may enjoy high fashion, but do you really want a designer gastric belt for Xmas? I didn't think so.

The good news is that a recent study by Dr Philippa Lally revealed some interesting facts about how to successfully form new, long-lasting habits. Together with her colleagues at University College London, she recruited people who wanted to get into the habit of doing something healthy, such as eating a piece of fruit each day or taking a 15-minute run.

Participants were then asked daily how automatic their chosen activity felt. Example questions were whether the behaviour was "hard not to do" and could be done "without thinking", and "What's that cream bun doing in your back pocket?"

Not surprisingly, the normal plateau curve occurred. That's to say, after a period of time either the habit was formed and became automatic, or it became too much of an effort and they returned to reading a copy of the Racing Post in the local snug. Typically, the plateau in 'automaticity' was reached after 66 days, by which time the new activity had become as much of a habit as it was ever going to be. However, although the average was 66 days, there was a marked variation anywhere from 18 days up to the thick end of nine months. I think as a teenager it took me about three days to form the habit of drinking beer, but I can't remember much about it now.

As you'd imagine, drinking a daily glass of water became automatic very quickly, but doing 50 sit-ups before breakfast required more dedication. So what does this research tell us? Firstly, never try to do fifty sit-ups whilst drinking a glass of water. It's not clever and it goes everywhere.

But perhaps more importantly, it revealed that when we want to develop a relatively simple habit like eating fruit or taking exercise, it could still take us over two months of daily repetition before the behaviour becomes a habit. And, while skipping single days isn't detrimental in the long-term, it's those early repetitions that give us the greatest boost in automaticity.

Now if you'll excuse me, there's something long and cool waiting for me in the fridge. Plenty of time for cutting back in the new year. Merry Christmas.

Philip Hesketh is a professional speaker on the psychology of persuasion and author of Life's a Game so Fix the Odds.