As the others have said – boat most interesting and is covered by a travel card. Otherwise overland train Waterloo East to Greenwich (may have to change at London Bridge) – this slightly slower than jubilee line tube but IMO easier.
Visit Cutty Sark too if you like your boats. Park and Obervatory too. Food market under railway arches at Borough (opposite London Bridge Station) is worth a stop.
If I were you I’d take the boat there and train back. If you are not in a rush on way back get off at London Bridge and walk along river past Borough market, Southwark Cathedral, Golden Hind replica, Shakespears Globe Theatre, Tate Modern, Waterloo