Most relevant one really was taking the plunge to return to university (aged 37) to do an MSc in a subject I really liked and would be a change of career (weighed up the pro's and con's - would be better long-term in terms of money but more importantly in terms of mental health), was working in a job that was literally killing me due to the effect on my mental health. I was depressed and when waking up in the morning actually dreading going into work, I knew that was not a good future.
Applied for the MSc (indeed, got a fully funded place AND a stipend equivalent to £1,000 per month net), took a year off work (later returned and took voluntary redundancy - so got a huge chunk of money kerching), did it - was fucking hard work, graduated and it's opened up a whole world of work that I find interesting, rewarding, decent pay and most importantly, I actually enjoy my job, I really like it. I don't have that black pit of loathing in the morning. The effect on my mental health has radiated into other aspects of life reducing my overall stress levels and allowing me to return to doing a fair bit of physical exercise which has knock on effects for positive mind and body.
The other best things I would say really are much earlier on in life that my mum taught me:
How to cook, cook from scratch, different methods of cooking - grilling/stir fry/making an omelette, choose and prepare food (meat, fish, vegetables), make a range of dishes, how to wash your clothes (you wouldn't believe how many people I met at university who couldn't boil an egg or operate a washing machine), how to iron (such an underrated skill - ironing a shirt quickly and efficiently is essential), how to do basic needlework (sew buttons back on, make a temporary hem (not so important now really), how to touch type (really handy in my work involving computing).
Best things I've also learned along life's pathway:
Develop resilience. Mental resilience, not giving up, this will develop your character and if you're a victim / weak willed all your life you're not going to achieve what you can. Or at least you can say you damn well tried.
Being realistic about matters and not a perfectionist. Sometimes realistic is good enough in the bigger scope of things.
Don't sweat the small things in life.
This thread is the most positive and uplifting I have ever read. A treasure trove of wisdom. Personally, I've a lot of contenders for "best" so won't choose. My partner (love at first sight), becoming independent in mind and deed, traveling the world, submitting to and passing various exams and tests, etc. Collectively they have enabled me to honestly say I could die tomorrow a happy man. And that is both wonderful and priceless.