Below is a collection of some tips I've learned to plan big, complex trips.
- Not planning at all doesn't seem ideal - planning roughly 2 weeks/1 month ahead would be the best. Tours can be booked latest 1 day in advance, but some of them can be seasonal so ideally you should check first.
- Weather forecast is important, try to plan indoor activities during days where it may rain.
- For long trips, there will often be a few days where you may not have the energy to do anything and just sleep or work. I think it's worth the trade-off to do that.
- What to see and do - getting advice from locals is the best, and also this is where AI can help you plan the trip. You can also get AI to plan a long trip covering the countries you like. Day tours can be a good option too if you do not have a car.
- At least 2 nights per country is ideal, especially if you are coming in from the airport since there is extra travel and wait time.
- I was happy to give up eating good meals for extra time travelling, and some days I only eat one or two because of time constraints, and live off of protein bars, breads and supplements. So think about what you could give up if you want to travel quickly.
- Leaving the city - if you plan to go to far flung places or small towns, it's often good to budget an entire day just being on the road.
- If you want to optimise for flexibility, maybe something like eurail or interrail would be useful.
- The sweet spot for couchsurfing is to ask about 1 week or so before arrival. You could try 1-2 days before, but it is hard for hosts to plan around that.
- For plane tickets, try to buy them at least a month in advance, or 1-2 weeks at most. It gets expensive after that.
- Carrying a simple backpack saves a lot of time instead of having a luggage. Try to pack as light as you can.
- Expect delays especially on trains and planes, so try not to have connections close together.