If you could offer your past self one bit of advice...

[Substitutiarylocomotion]

That was not do to with romance/relationships...what would it be?

Don’t ever smoke

Move away

Seize every opportunity and try new things.
Don't pay attention to what people think.

Travel.

Be super focused on your career.

Never, ever go on a diet or try to lose weight.

Get active and stay active

Hold on tight to your dreams ... live "your" life no one elses

Do the A levels you're interested in, not the ones the teachers push you to do because you're good at them.

If you have the slightest feeling it’s not right, walk away early.

and also get counselling, for anything you found hard. It will come back and haunt you in later years and interfere with your new life

Start a pension.

Don't be embarrassed about the things that make you who you are.

Always listen to your gut.

To not care or bother about what people think or say about you.Unless they matter to you and have your best interest at heart.

Two things: get a decent education and deal with issues when they arise because sticking your head in the sand means they get bigger along the line

Your parents approval is not important. Just be happy and do what you want

Don't let anyone else make decisions about your future for you. If you are unsure what you want to do, take some time to figure it out before committing to expensive degrees.

Trust yourself. Everyone else is more stupid.

This.

Dont marry exDH. Take more development opportunities at work before I had kids.

Go out of your comfort zone

Believe in yourself more and be confident

Just fgs don’t be such a dick

Not to go all Baz Luhrmann - but wear sunscreen daily. Even when it's cloudy in the UK

Dont try to make everyone else happy or comfortable at your own detriment.