Life is too short to waste it in a job or relationship that is making you unhappy. There will always be other jobs, partners and opportunities although it may not feel like it at the time.
You are never too old to learn something new, to try different things or to change direction. If teaching/stockbroking/insurance/retail is making you miserable then think about what you want to do and plan how you can get there.
Don't be afraid to give up on something if your heart isn't in it. Although I have the odd regret about giving up on my MSc the sense of relief when I decided I'd just had enough and was totally and utterly bored rigid with it and chucked the study material in the wheely bin told me I'd done the right thing.
Always treat people as you would want to be treated yourself and avoid those who don't treat others with respect.
Be a caring and generous friend/relative/partner/employee/employer/ but know when you are being taken advantage of. Learn how to say no and mean it.
Don't do drugs and don't start smoking. Work to live and not the other way round.
When you're thinking about buying property always go for the worst house in the best street rather than the best house in the worst street (My former colleague's bank manager husband gave me that gem)
Get a dishwasher. Spend ten minutes before you go to bed every night having a quick tidy up. Getting up/coming home to an untidy house is depressing. Keep up to your laundry. Buy as many clothes that don't need ironing as possible. Invest in a Miele vacuum, don't waste your money on a Dyson.
Take the opportunity to relax, chill out, enjoy the company of family and friends whenever you can. The older you get the more these moments will become precious to you and will become memories you will treasure.
And give your Mum a great big smacker and a bear hug. She sounds absolutely lovely and I wish I'd thought of such a special gift to give to my boy. Happy Birthday x