I agree with the above points. One thing that I cannot stress enough is that songwriting is no different than playing an instrument. Where as some people may swing more towards certain aspects of music than others, the bottom line is that it does take practice. But, once practiced enough; you can capture the creative process much quicker each time as well as being able to find inspiration a lot easier. Think of it as if you were practicing your instrument; involving writing lyrics, melodies and chords. Frank Zappa used to treat writing as a day job, working 8-12 hours on that alone (not to mention all his other musical and theatrical duties.) Again, the more you do it the easier the inspiration comes and the better the songs get. Don't just wait for things to fall out of thin air.