Coaches arrive at Gloucester Green bus station. There are regular direct services from London, Heathrow airport, Gatwick airport, and Cambridge. There are also less frequent services from Stansted airport, and many other destinations in the UK.
When you leave the bus station, walk to the top of George Street, and turn left onto Magdalen Street. Walk past Debenhams, and cross the road by the Randolph Hotel. Then follow the general directions within Oxford.