Paris Without the Queues: A Practical Timing Guide
Book timed entry, always
The Louvre, Musée d'Orsay, and the Eiffel Tower all sell timed-entry tickets online, and the difference between walking straight in and waiting two hours is entirely down to whether you booked ahead. Do this the moment your dates are fixed, not the night before — popular slots (especially Eiffel Tower sunset) sell out days in advance.
See the Eiffel Tower from the ground, then leave
Going up is expensive and the line is real even with tickets. The better version of this experience, honestly, is Trocadéro at night: free, no line, and the view includes the tower itself lit up, which you obviously can't see while standing inside it.
Montmartre before 9am
Sacré-Cœur and the surrounding streets are genuinely charming and genuinely overrun by midday. Go at opening time instead — you'll have the steps to yourself, and the cafés are just opening, not yet turning tables for tour groups.
Eat lunch, not dinner, at the place you're excited about
Many of Paris's best-regarded bistros run a fixed-price lunch menu (menu du jour) that's a fraction of the dinner price for nearly the same food. Reservations are also far easier to get for lunch — a good way to try a restaurant that's fully booked for dinner three weeks out.