My biggest tip when traveling from London would be to check and book ahead on train and bus tickets. We booked tickets online on the Oxford Tube bus. The bus originates at Victoria station and leaves every ten minutes during the day. We got on at Notting Hill Gate but it also stops at Marble Arch, Hillingdon and a few places outside of Oxford. A day return ticket is £15. Other options include the Oxford Express bus and direct trains from London Paddington. The bus takes about 1.5 hours and the train about an hour.
Christ Church College and Cathedral is open until 5.30pm but last entry is at 4.30pm. You may want to check ahead to see if all buildings on this and other tours will be open at the time you plan to go. If you’re hoping to do a walking tour or bus tour you should also check ahead on availability.
Finally, when we were in a souvenir shop, the shopkeeper was alerting a customer to pickpockets that work Broad Street. Being in such a charming place it is easy to become distracted but unfortunately you do need to keep a close eye on your belongings.