Oh well, I am not from Lisbon, and dont know it that well, but I would say you must visit the old areas like "Bairro Alto" (get some drinks there at night 😛), Alfama go listen to some "Fado" music, go see the castle S. Jorge, go see "Mosteiro dos Jeronimos" take a coffee during the day at "Adamastor"... hmmm if you really like historic "fairy like" places go one day to Sintra (no very far from lisbon, about 30 km or less), etc etc
At least one of the members here in RFF is from Lisbon, and if he gets online he will tell you good places to go and shoot 🙂 (he is having problems with internet)
I live on the northern part of Portugal, near Oporto, so cant help you any further...
I hope you enjoy your stay and like my country (not sure when you are comming here, but this year the winter is quite cold)
Sergio