Backtracking across the city
Two museums in the same district visited on different days can cost ninety minutes of transit. Grouping activities by neighbourhood is the single highest-return optimization in trip planning.
Ignoring opening hours and queue patterns
Popular sites have predictable pressure windows. Moving one visit two hours earlier often removes a forty-minute queue, and the rest of the day inherits the saved time.
Over-scheduling the first day
Arrival days are travel days. Planning three activities after a morning flight reliably produces one cancelled activity and a bad dinner.
A concierge that knows your arrival time should protect that evening rather than fill it.
No weather alternative
Every outdoor block should have an indoor substitute nearby. Deciding it in advance keeps a rainy afternoon from becoming a wasted one.
Booking food last
Restaurants near an activity, in your budget, matching your diet and open at the hour you will actually be hungry is a small optimization problem. Solving it while planning is far easier than solving it while walking.