Add the fixed points first
Begin with flights, trains, check-in times and booked activities. These anchors show how much free time each day really has and reduce accidental clashes.
Keep ideas separate from commitments
A good itinerary leaves room to change your mind. Add possible restaurants and attractions without making every suggestion feel like a fixed appointment.
Make it useful on the move
Keep addresses, times and notes beside each activity so nobody has to search old messages at the station or outside a restaurant.