Obviously you need high inspiration. It seems that the song options with the Bass notes add more to the quality to the song. If those aren’t available, it seems the choices with 3 notes (as opposed to 2) are a better bet. Aside from that, are there any other strategies to making better songs? I’ve never gotten anything higher than 84%. Are there certain spots that need certain types ?
-complex notes are more valuable (3>2)
-match colors (1st notes end in [color=red]red, 2nd notes start in [color=red]red end in [color=blue]blue, 3 notes start in [color=blue]blue… etc)
-have inspiration, as you say
-musicianship prob’ly helps, too
-you get better with experience
-take a break (writing too many songs in a row leads to burnout)
-some days are better than others
[edit] Also, attend other bands’ shows and buy/listen to CDs from the store to ‘unlock’ new song-pieces [/edit]
to confirm what Prosayist wrote and add my experience…
because with more pieces you have a better chance to have more matching complex -4 or even 5 notes- song-pieces
to make almost perfect quality songs
(So far the best quality i could make was 95% 
)
musicianship seem to allow for the more complex notes to appear more often.
But even if your musicianship is high and inspiration at 100% after the 2nd and 3rd day of composing new songs the quality of the notes gets really low. (the so-called burnout).
@cliffski : an option to start with an empty paper would be really nice !