Fa Do Sol Ré La Mi Si
(F....C....G....D...A...E...B)
this is the order in which sharps go. Gives you the tonality of a given song. Let's say the song takes 4 sharps- take the last one (Ré/D), add a half-tone to it (Mi/E), there it is, your song is in E major
It works with flats as well, in the reverse order (Si Mi La Ré Sol Do Fa). Take the next-to-last flat, that is your tonality.