Get a pension as soon as you start working and pay the max possible in that you can, to get employer contributions. Move all your 'old job' pensions into one platform so that you can keep track. Compound interest is a very real thing, but it takes (a lot of) time
Always keep separate bank accounts (outside of any joint bill accounts) if you do get married / live with someone
You don't have to have kids
You don't have to get married / live with someone if you don't want to
You have to work at friendships to maintain them, but some you can pick up after 10 years mostly radio silence, if they were good friends to start out with
You don't have to do things 100% perfectly. Work out what is 'good enough' (may vary depending on what you're doing and the circumstances) and do it
People really don't care what you are wearing or doing etc, they are wrapped up in their own little world
If you turn up for work and get on with it, it's not enough. If you want a payrise / promotion, you have to do the networking as well. Or, just move roles every 3/4 years
Pick a career, not just a job. Pick something which you can get qualified in, and which will give you a steady income stream no matter what stage in life you are at. Don't pick it to satisfy parents / teachers / OHs etc, you are the one who will be doing this job. And it doesn't have to be the best job ever; it just has to be one which you can tolerate turning up for work each morning and which you enjoy enough.
Find a sport / activity that works for you, and do it. For a long time I cycled to work as it was cheaper and quicker - I wasn't 'a cyclist' though. Now I swim as I love being in the water. Don't feel like you have to run / yoga / other activity just because everyone else does it
Speak up for yourself. No one else will, and most other people are looking out for themselves and won't think of you (not maliciously, they are just looking out for themselves).
And finally:
No is a complete sentence.