i find that when i'm bogged down with work and have my mind on other stuff, i just can't be creative. but when i make time for trying to play the guitar and write lyrics, every once in a while something good will come. as far as lyrics, don't worry about stuff ryhming too much, most good songs don't ryhme every single measure anyway i find. u have to just find the words that fit your song the best. usually you'll need to make small adjustments to make them fit perfectly.