Planning your itinerary

Google calendar is a useful tool to plan your itinerary while traveling. It's primary usefulness comes in the ability to quickly add, move, and delete your schedule to see how everything all fits in.
My first steps when planning is to find a range of dates that I can take vacation. Once flights are booked I mark down those anchor dates. Then starting high level (what countries will I be in during these date ranges, then what cities, then what plans will be for each city. If it's a hectic day with lots of things planned, I'll even go into an hour by hour schedule, especially for things you had reservations for.

I'll also the week before or after I'm traveling add extra things that I'd like to do but aren't a priority in case something changes (like bad weather / good weather, etc)