In the often-woolly world of personal development, Gretchen Rubin is a practical and grounded sort. She doesn’t even – shock – like meditation. Rubin has spent the past decade researching and writing about happiness. A former lawyer, it was her fifth book, The Happiness Project written in 2009 – for which she spent a year testing different theories about how to live a more fulfilled life – that became a bestseller and made her a star of the self-help world (she also runs a popular blog and podcast).

Her latest book, The Four Tendencies, develops ideas first explored in 2015’s Better Than Before, in which she looked at how happiness and habits were linked. “[People] wanted to run,” she says, “but for some reason they couldn’t make themselves exercise. Or they wanted to write a novel in their free time, but somehow they weren’t doing it. It was trying to figure out why people did and didn’t break habits.”

She came up with her own personality framework – the idea being that each of us fits into one of four characteristics she calls the four tendencies. Rubin claims it explains the reasons behind why we do what we do, based on how different people respond to expectations – either outer ones (from, for example, a boss at work) to inner ones (things you want to do for yourself). According to Rubin’s categories, “upholders” easily do what is asked of them by themselves and others, while “obligers” need accountability. “Questioners” need to know why they’re doing something and “rebels” resist expectations. She says she truly felt that “I’d uncovered a law of nature: human nature”.

After Better Than Before came out, Rubin says, she was, “deluged with questions” about this idea. Thousands took her online questionnaire to work out what type they were, and she started to wonder if our tendency had much more influence over our lives than whether or not we could stick to a diet. “It’s related to habits, but it’s much bigger than that,” she says on the phone from her home in New York. “It might also shape something such as having a fight with a co-worker, or having a better way to communicate with your child.”

The result is her new book, which explores her theory further, and provides advice on how to deal with the four types. She says the failure to understand other people’s tendencies can be responsible for everything from relationship breakdowns to failing public health campaigns, and that working with other people’s tendencies can improve the way bosses and employees relate; help doctors encourage their patients to take control of their health, and help teachers get the best from students.

The biggest thing she has learned in more than a decade of thinking and writing about happiness, she says, is that “there is no one-size-fits-all solution. We can only be happy, healthy, creative and productive if we take into account our own nature, our own values and interests. The question is: what kind of person am I, what works for me, what do I care about?” Even so, Rubin is game for creating rules and lists (she’s an upholder). What, then, are some of the things she has learned on her quest for a happier life?

Create your own principles

In The Happiness Project, Rubin created “12 commandments” by which to live her life, including “act the way I want to feel” and “enjoy the process” – but she stresses that someone else’s list will probably be different. “My first personal commandment is to ‘Be Gretchen’, because in the end there is no one best practice, there is no best way,” she says. “When I started, I thought I would find the secret [to happiness]. There are universal things – relationships make people happier. But in terms of should you get up early, or stay up late? Are you more creative if you’re in a messy environment or a simple environment? It’s so much about who you are.”

Test yourself

2009 study by San Francisco State University found that learning to do something new could be stressful and frustrating to begin with, but paid off in terms of greater overall happiness. “I thought ‘oh no, I like familiarity and mastery’,” says Rubin. “I just felt like it wouldn’t be true for me, but I have become a huge believer in the power of novelty and challenge and how this is a big engine of happiness.”

Declutter

“Another thing that surprised me is the degree to which outer order contributes to inner calm. Over and over people tell me that if they get control over the stuff of their life, they feel more in control of their life generally. They feel more energetic, creative, they can tackle bigger things. Somebody said to me: ‘I cleaned out my fridge, and now I know I can switch careers’. There does seem to be a connection for most people, but not everybody.But if you want to give yourself a boost, sometimes clearing clutter can help.”

Look after your body

“Your physical capacity matters – getting enough sleep, getting some exercise, getting natural light, not letting yourself get too hungry.” If you are starting from a position of feeling comfortable and rested, she says, “you give yourself a lot more wherewithal to tackle things such as staying patient, not losing your temper, eating right, going to the gym – all these things take energy and self-command, and they’re easier if you manage your body”.

Seeking happiness is not selfish

“This comes in two different varieties,” she says. “One is that you think: ‘My life is so full of comfort and security already so if I want to be happier, I really must be spoiled and self-indulgent because I already have so much.’ The other is to think, in a world full of suffering, that it’s not morally appropriate for people to seek to be happier. But research shows that happier people are more interested in the problems in the world and in the people around them. They’re more altruistic,they give away more money, they volunteer more time, they are more likely to help someone who needs a hand. They make better team members, they’re healthier, they suffer less burnout. When people are unhappy they tend to become isolated, defensive and preoccupied with their own problems. When you’re happier, you can turn outward and think about other people.”

The Four Tendencies is published by Hodder & Stoughton (£14.99). To order a copy for £11.99, go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min. p&p of £1.99.