I normally just make them up on the spot. Or I will write the title first and make music to evoke it. Sometimes the title will talk about the mood of the song ('Oceanus Procellarum' is the proper name for the Ocean of Storms on the moon, the track is bleak and spacey therefore etc.) sometimes it will be a literary or other reference I have collected which I either write the track to fit, or I think fits in with the track after its finished for one reason or another (The song 'His Hair Was of a Lustrous Black' is all about Frankenstein, and is a line from the description of the monster in the original, 'Starless and Bible Black' is a line from Under Milk Wood (not a King Crimson reference), 'What Did the Romans Ever Do For Us?'...well, you know). Other shit (ie. 'Forensic Musicology', 'Huxley Orwell Overdrive') are just stupid puns or shit I make up.