Plan, plan, and plan some more. Things will not always run to plan, but you won't be worried because you will have lots of information and so many options already researched. Paradoxically, planning allows for spontaneity during your travels. Plus learn to love that planning phase for all the things you will learn.
If I were allowed more than one thing I've learnt, I would add:
- things are different. Not better, not worse, just different.
- people are people, wherever you go. There will be absolutely amazing, kind, generous and lovely people, and there will be total asshats. That is a reflection of those individuals, not of their country, culture or religion. They might just have had a bad day too.
- influencers don't know everything - be bold and find your own places and activities.
- try local foods and drinks - cheaper than eating like you were at home and often amazingly delicious
- when things don't go to plan, breathe, and then make the best of things. If a flight or train or bus is cancelled, it is cancelled. And having a tantrum or a panic attack won't get it uncancelled. Use some of your prior planning to make a new plan, and then enjoy what comes your way because of the new opportunity.
- if you can afford it, book things that allow for free or cheap cancellation - this gives you a lot of flexibility and some peace of mind.
- ask for help if you need it. Better to ask for help while an issue is still small than let it escalate.
- if you can't afford travel insurance, you can't afford the trip. And read the boring but important small print about things like having a motorbike licence to ride a scooter in Bali, the effect of too much alcohol on your ability to claim for related injuries of lost property, the need to declare anything at all that you have seen a doctor about in the last 12 months, etc etc.
- read smart traveller for lots of good advice.
- you will come back a different person after a trip overseas. You will see your home country differently (for better and for worse). Other people, including your parents, may not realise this, which can make it hard to be home again.
- watch out for the travel bug. Once it bites you, you are addicted for life.
Useless advice: have fun!!