What advice would you give to a first-time solo traveller?

trust your gut, go with confidence, use common sense.

Plan where you're going carefully.
Plan alternatives should transport or weather hamper your progress.
Make sure you know the law for each country you visit ! Simple things like leaving the soles of your feet exposed can land you in a whole lotta trouble in some places !
Obviously don't flash your cash; phone; passport; camera in public.

When in a foreign country and eating out. Don't ask to replace an item with another item. Either accept the plate as is or just don't accept it at all. You will rarely get what you want maybe worse.

If you're going solo, then the most important thing is to be open with everyone and also be careful at the same time

Don't put all your money together in one spot on your body.

Keep your wits about you.

Just be safe.