So this time next week we will be in Prague (!!) for the first time. I have a couple of walking tours booked but am wondering if there are any of the major sites that should/can be booked ahead to avoid lines?
If you plan to visit the castle and St Vitus Cathedral, Rick Steves has good tips about when and where to get your ticket ( early morning near the cathedral itself.) By following his guidance, myself and 1 other person enjoyed 10 or 15 lovely and quiet minutes going through the paid section around the inside perimeter of the cathedral before throngs began arriving.
If you book an Old Town Hall visit online via the official portal at https://prague.mobiletickets.cz/ that will be cheaper than paying at the ticket office and you'll skip any ticket queue but you'll still have to queue up the top of the tower. It's not something that you need to do a week in advance though. Likewise if you go to the zoo then buy entry via https://vstupenka.zoopraha.cz/ and you use a QR code to bypass the ticket office.
If you want to visit the Jewish sights, note that they close around 1 pm on Friday and only reopen on Sunday. Because of the resulting backlog, Sundays tend to be very crowded.
Municipal House (Obecni Dum) has a beyond-gorgeous Art Nouveau interior. Tours are offered in English and can sell out. I don't know whether you can book ahead online or just need to wander past the building at the beginning of your trip and check on the schedule. If you have any interest in indoor photography, pay the extra fee. I regretted not doing so.