If you are travelling from the UK the ferry MV Jupiter leaves from Newcastle International Ferry terminal, twice a week. It then goes on to Bergen through the fiords, before returning to the UK. The sail through the fiords is worth the trip itself.
We took the ferry from Bergen to Stavanger. That is easy to do, brings you from one city center to the other. Its a 4 hour trip by catamaran.
We had the bad luck that the weather wasnt good, halfway the trip in Leirvik we had to leave the ferry to get on a bus to Haugesund. There we left by ferry again to fullfill the trip to Stavanger.
See for the Ferry Newcastle Upon Tyne UK, to Stavanger, Haugesund and Bergen, my Bergen Transportation tip.