I personally hate rhyming my lyrics, its not that I have trouble doing it I just feel that it seems contrived and fake, I do rhyme when I feel it makes sense to or just naturally fits, but I try to come up with interesting things to say and use words that express the image better rather than saying, this phrase has to end with this rhyme and force my lyrics into a mold.

as for music it depends on what Im writing for, if its a heavier song than I usually can hear what I want in my head before I try to figure out how to play it. For other stuff I usually just come up with a simple progression and then expand upon that.

Does anybody else have the problem of having tons of very clear ideas for riffs and melodies in your head and then you go sit down with your guitar ten minutes later and you can't remember any of it, and not only that you can't think of anything at all. This happens to me sometimes and its annoying as hell, I've taken to carrying a recorder around with me in case I suddenly get an idea because I know I wont remember it the second I sit down.