In any case, here as everywhere in the world, the "golden rule" usually works well: be polite and smile!
Here you have some useful words/expressions:
English / Catalan / Spanish (Castilian)
Hello / Hola / Hola
Good morning / Bon dia / Buenos días
Good afternoon / Bona tarda / Buenas tardes
Good evening / Bona nit / Buenas noches
Thank you / Gràcies / Gracias
Please / Sisplau / Por favor
Excuse me / Perdoni / Perdone
I'm sorry / Em sap greu / Lo siento
Goodbye / Adéu / Adios
See you later / Fins després / Hasta luego
Hi, I don?t speak Catalan / Spanish, do you speak English?
Hola, no parlo Català / Castellà, vosté parla Anglés?
Hola, no hablo Catalán / Castellano, usted habla Inglés?
If you're interested in learning some Catalan expressions, the following links is an online conversation guide where you can hear the words/sentences (oriented to foreigner University students, but may be useful to any visitor):
http://www.ub.edu/guiaconversa/angles/a.php?fer=GUIA&idioma[]=1&idioma[]=7&ordre=7

