I use several methods depending of the type of music I'm creating...
For piano/organ pieces I play and play in piano looking for good material but not just random notes, I play somekind of improvisation using the material I already know is good, or I know how it sound, like chords progessions, motifs, some of those are inspired on music I've listened (other composer's works) in other words, based on what I have learned.
for orchestra I write directly on Sibelius, I write a line in some instrument (based on what I heard on my mind or what I discovered on the piano) then I play it, listen it, and write on another instrument what I heard on my mind while listening the Sib playback, then I play again the two lines/motifs and I heard more things in my head, I add them and so and so, like creating layers of lines/motifs in instruments/sections ... then I construct the following parts of those lines/motifs, .... after creating a significative part, I play it all from the begining and I edit/add/delete things according with the result I just heard..... rarely I listen all in my head and I open the Sibelius to write it all, already designed or created.
for Electronic pieces is about the same, I just switch my way of handnlig harmony/melody/beat using the other elements I know from the Dance/Pop/Trance/Rock music I've heard, the song I know/like but I also add things after listining the playback results. Rarely I just add random stuff for creating "Experimental" music.
so, basically the "quick results listening" is very important for the ñast two methods, ... if I wouldn't have the way to listen what I write (as in my old composing days) my orchestration would be easier and simpler, wrinting only what I'm sure of how does it sounds...