Museums or Basilica?
The Vatican Museums and Sistine Chapel require a ticket and a timed visit. St Peter's Basilica is free but has security queues. If time is short, choose the Basilica plus the square, or book the Museums early.
Best time to go
Early morning is best for the Museums. Late afternoon can work for the Basilica. Avoid Saturdays, Mondays and free-entry days unless saving money is more important than comfort.
Dress code
Cover shoulders and knees in the Basilica and Vatican spaces. A light scarf solves many summer problems, but shorts that are too short can still get refused.
Common mistakes
Buying overpriced tickets from street sellers, arriving without water, planning the Colosseum the same afternoon, or assuming St Peter's is inside the paid museum route.