What's the best way to get from the Dubrovnik airport to Mostar? And is a tour guide needed in Mostar?
For a day trip or overnight?
Reading might be sufficient for you, but a tour guide is never a bad investment.
There is a bus from Dubrovnik, airport bus would connect you to the bus station.
For an overnight, the bus works great. If you are trying to daytrip, that is a bit difficult by pubic transport, you would need an organized tour. We took the bus, stayed overnight, then went on to Split by bus the next day.