@Nick Did you mention Greece ? ??Where's that? It must be in my dreams !
My planning starts with
1. Internet searches for flights, times, hire cars or public transport.
2. Location of accommodation near public transport or out of built up areas with a hire car.
3. Accommodation prices within budget and what the accommodation offers.
4. Bathrooms as @Liv points out. After several trips to UK and Europe I have to now check out the showers as some need instructions a bit outdated or insufficient water supply and you dont find out till you use them.
5. Accessability in accommodation, as in a number of stairs to bedrooms or to bathrooms.
6. Interests as @Helen427 mentions and the reason why travelling.
7. Wi Fi access
8. @Gordon0 great idea for a photo copy of Covid positive test results and I would add a copy of vaccination dates as we don't have a vacination passport downunder yet. I also copy bookings for accommodation, flights, insurances, passports, drivers licence, pension cards all on recycled paper. I know I may be over cautious but it is a long way home if everthing is on your phone if lost no sim card or not working.
Lastly, this is a wish list for me, I can't even travel to some local region areas, or states within Australia let alone visit daughter in New Zealand. But you could say we are lagging or behind the northern hemisphere.