I would echo all y'alls points. The big thing for me is that you got to get rid of any hangups or stop taking yourself too seriously when writing music. If you do all of that you become like the Onion headline said:
Experimental Band Theoretically Good
Just finding a way to relax and go with whatever flow is floating your boat along is the best way to write. You can tackle a serious subject with sincerity by using simple terms you understand, no one wants to hear some Shakespearean word-play if we can tell you don't mean it. When all else fails if you dig the sound of the song but can't find the words... make sh*t up, hell early Pink-Floyd, the Beatles-psychedelia, Bob Dylan, Brian Eno all put nonsense words together and made great music because of that. I know I struggle doing this but I've seen that when I do manage to do all that some pretty great stuff gets saved on the hard drive.
I forgot to add, if you're really into lore and mythic sh*t write about hobbits and the like. Hell look at Zep and early T Rex! that's all they did and they were rich and famous...