Volunteers who were asked to recall a pleasant event from the previous day were given an immediate 15 per cent boost in happiness
Other techniques that helped to increase happiness included expressing gratitude, smiling and carrying out an act of kidness.
The research found that 65 per cent of those recalling something happiness had a boost in happiness, compared to only half of those who just thought about the day's events.
An act of kindness led to a nine per cent boost in happiness, while being grateful for an aspect of life led to an eight per cent rise and making an effort to smile and hold it made people six per cent happier.
Professor Richard Wiseman, from the University of Hertfordshire, conducted a mass-participation experiment online, with more than 26,000 people joining to try recognised mood-boosting techniques.
The "happiness experiment" was set up in an attempt to send cheerfulness across Britain.
Together with a nationwide publicity campaign which saw Prof Wiseman give 30 radio interviews, it was hoped the experiment might make Britain a happier place.
To find out, a ''before and after'' survey was conducted among a representative 2,000 people from across Britain.
It showed a 7 per cent increase in overall cheerfulness after the experiment.
The figure is statistically significant, said Prof Wiseman. I thought with a representative sample you wouldn't see a change, but we got a 7 per cent rise.
There was no big improvement in the weather or anything in the news that could have accounted for it, and we looked for that.
Who knows, but I like to think we might have cheered up the nation
Participants were asked to carry out the tasks every day for a week and report any changes in their happiness, as well as that of people around them.
All of the techniques, including the control, resulted in a reported rise in happiness
However, thinking about one positive thing that had happened the day before appears to have been by far the most effective technique.
Compared to those in the control group, this quick and simple procedure provided an additional 15 per cent boost in happiness