You’ve got the Headspace app, know your downward dog from your black dog, and once read something by Freud, so what can a guy who lived 23 centuries ago tell you about the pursuit of happiness today? “Aristotle did it first and better. So why not go to the source, the original brain that figured all of this out?” says Professor Edith Hall. “I think there is a comfort in ideas that people have held for thousands of years.”

Her book, Aristotle’s Way, promises to teach you “how ancient wisdom can change your life”, in particular how to achieve a lifelong state of what the ancients referred to as eudaimonia and we come closest to with “contentment”. According to Aristotle, Hall writes: “The ultimate goal of human life is, simply, happiness, which means finding a purpose in order to realise your potential and working on your behaviour to become the best version of yourself.” It’s an ancient version of that poster “Work Hard & Be Nice to People”, but in a less cool font.

Aristotle approves of food, drink and sex (all in moderation – he’s big on moderation); he believes leisure is more important than work; that we all have innate talents and that we don’t peak until we’re 49. What’s not to like? But by far his most significant claim is that happiness is achievable by almost everyone – you just have to “decide to become happier”. Simple, huh! “Happiness is not a state as far as Aristotle is concerned, it’s an activity,” Hall explains. “You have to do it. It means every encounter and every day of your life and every decision you take, trying to do it in a measured and deliberated way until it becomes habitual.”

Like anything, happiness just takes a bit of planning, Hall argues. “Plato, his teacher, said that the unconsidered life is not worth living. Aristotle would say the unplanned life is slightly less likely to be happy. It’s planning. Just planning.”

With all the injunctions to become the Best Possible You, Hall clearly has an eye on the self-help market as well as both feet firmly in the classical world; you almost expect to find a photo of a toga-clad Aristotle smiling beatifically over a slice of avocado toast. “Virtue ethics” doesn’t sound much fun, and Hall gamely breathes new life into his doctrines (which she admits can be heavy-going) for 21st-century readers, flitting over the centuries and across cultural borders, taking in everyone from Philip of Macedon to Pharrell Williams of “Happy” with breezy aplomb. A beguiling cross between Mary Beard and Mary Poppins, Hall is enjoying herself outside the ivory towers: “I love the idea that I’m now in agony aunt territory with Aristotle.”

The daughter of an Anglican priest, Hall lost her faith when she was 13 and spent the rest of her teens in a “moral wilderness”. When the rest of us were experimenting with cigarettes and blue mascara, Hall dabbled in astrology, Buddhism and transcendental meditation in an attempt to answer her fundamental question – why be good? “If you don’t believe in an interventionist God or an afterlife, there is no logical reason whatsoever to be virtuous. Why would you not just pursue your own self-interest?” Then, as an undergraduate at Oxford, she discovered Aristotle: “I decided this was such an unbelievably commonsensical way of trying to organise your life. I was blown away. It was a total epiphany. So I just started doing it, as it were.”

Planning and moderation aren’t the first qualities we associate with students, and Hall admits it was tricky at first. “It’s terribly grown-up to take complete responsibility.” And here Aristotle is characteristically forgiving, arguing that humans aren’t capable of consistent rational forethought until they are at least 25 (something now backed up by research, Hall points out). And it took her until her mid-30s to realise that if she wanted to fulfil her hopes of becoming a mother, she needed to stop dating “handsome lizards and moral invertebrates”. She now has two daughters, one of whom also loves history and who accompanied her on a tour of Greece in the footsteps of her hero.

So what does doing it actually mean? Being nice is “not just a matter of enlightened self-interest”, Hall says. “There is an intrinsic wellspring of good feeling about yourself that does actually supply a feeling of contentment.” The examples she gives are making sure she always smiled at her children “however tired, however annoyed” she was, or taking a purse to the police station or lost property, “when the temptation might be to put it in your pocket… It may hurt a bit, but you just have to start making yourself do it.”

If, like me, you come over all anxious at the idea of not handing in a purse, or apologise five times when someone else bumps into you, then you may be what Aristotle calls “an intuitive virtue ethicist”. Who knew? “Good for you!” says Hall, in a way that doesn’t sound so good. You can be “too nice” to be a true Aristotelian: not enough anger, for example, is a problem, especially for women. “It means you have no self-respect, will get walked all over and won’t look after your own. It’s not OK. You can’t be a fully moral person, actually.” Oh dear!

One of the joys of Aristotle’s philosophy is that it works whatever your age, Hall believes. But she is evangelical – she describes herself as a “secular missionary” – on the need to offer moral guidance to young people, on those crucial everyday things you don’t get taught at school. “Taking a decision, clear communication, how to use your leisure, how to choose a partner and friends, and when it is absolutely fine to get rid of friends.”

If it all sounds like doing what your mother always told you – smile, do your homework, everything in moderation, whatever! – there’s the rub: while we may have been well loved, Hall thinks we have not always been “well parented”; we are failing our young by inadequately training them in basic decision-making skills. And so her book includes practical advice such as how to write a decent job application and when to dump your partner.

What are her top three tips for getting in touch with your inner Aristotle?

Number one: “Be honest – know your vices.” Hall provides a handy version of Aristotle’s inventory of character qualities, a sort of personality quiz. She identifies her own worse fault as vindictiveness. “I like to get back at people if they’ve hurt me or my loved ones. I enjoy it,” she smiles dangerously. Now, as an enlightened Aristotelian she only goes “out for revenge when it is appropriate”.

Number two: “Review all your relationships”, which should all be based “on full-blown reciprocal trust”, according to Aristotle. He has a system for dealing with friends and relatives who don’t come up to scratch – you simply demote them according to his categories “primary”, “pleasure” and “utility” (“I occasionally meet them for lunch,” Hall says of a couple of her relegated rellies). The latter might sound like something you have to assemble from Ikea, but it amicably encompasses most of our friendships.

From your spouse to society at large, all relationships are contracts, apparently. What if your partner cheats on you? “I would always give them one more chance,” says Hall. On adultery, Aristotle “talks rather too often about the problem of fancying your neighbour’s wife”, she says. But his belief that if you abuse marital trust “you are actually rotting the foundations of society” has certainly helped her to be “a good girl”.

Number three? “Think about your death. Look to the end,” Hall says emphatically. “Because it makes you get on with things. It’s about thinking of your life like a biographer while you are doing it, that your life is an art.”

While the idea we can simply choose to be happy is seductive, it is rather in the “chin/socks-up, it’s-all-in-your-head” school of psychology. We can hardly blame Aristotle for being a little old-fashioned (he was also dodgy on women and slaves, which Hall excuses by arguing that he was always open to changing his mind).

But taking responsibility for your own happiness will be of little comfort to the clinically depressed or recently bereaved. Hall agrees it can be difficult, but not impossible for people to find gratification after terrible tragedy, and ultimately, she says cheerfully, life is pretty bleak: “We are all in a waiting room. It’s just whether we decide to spend it trying to have a wonderful time with each other.”

Aristotle’s Way by Edith Hall is published by Bodley Head at £20. To order a copy for £17, go to guardianbookshop.com