Me personally, inspiration comes at odd times and for no apparent reason. What I've found is that listening to other people's music does nothing for me (on an inspiration level). My only advice I can offer is don't force it otherwise it'll show. (You might want to watch the Tenacious D short "The Search For Inspirado") And try to only write what you know, don't try to write a song like somebody else, I've stuck to this rule so closely and I think I'm a better songwriter for it (Although I'm sure there are many who will disagree.)
I tend to write about obscure things so it doesn't matter what I write as nobody can argue a point that I don't know what I'm on about. I find it hard to write 'serious songs' as my songs tends to have an edge of humour and any meaning is then lost on the listener.
Some of this post may be irrelevant but it's nice to type