Try and tell a narrative. The songs should be like a little film, told in three or four minutes. Try to say things as simply as possible, which is probably the most difficult thing to do. It's easier to say things in a complicated way than to take the same thought and say it well but simply. The more you work at this, the better you'll get. There has to be a basic truthfulness in the lyric that people can identify with. Otherwise it won't move or touch people. Find your own voice, don't copy what other people are doing. And don't try copying the latest thing - today's big hit will not be tomorrow's big hit.
Ideas can come from all sorts of sources, in most cases they're subconscious, but read books, go to films, listen to people talking, and you'll find lines or phrases sticking out which lock into your mind. Many years ago, when I was in London, I was supposed to be going to a dinner party and I called to find out what time I was due, and the hostess said: "When you come, don't ring the bell, just come up, that will make one less bell for me to answer". That last phrase became the title of one of my songs. That happens. When writing lyrics, it's important not to take the easy way out - know that there's something better than the first thought or first line you had, and keep digging through until you find something that you can really feel proud of.
Hal David, lyricist of "Raindrops Keep Falling on My Head" and "Walk on By", amongst others, has recently won the Special International Award at the Ivor Novello Songwriting Awards