Generally

1. Read a travel guide (like Lonely Planet or Rick Steves) for an idea of an itinerary

2. Read travel itineraries on Reddit or Google search

3. E-mail travel writers from the guide books and book a paid 1 hour zoom session to refine itinerary (I have found this to be extremely helpful)

4. Create a google docs and sheets of the itinerary

A new thing I've been playing with is ChatGPT to generate an itinerary