Can't get started? Listen to some music: I often find that a good way to get started is to play some CD tracks in the style I'm looking to write a song in. This doesn't prompt copying, subconsciously or otherwise, but it fills my head with music patterns, chords, sounds, etc., and puts me right in the mood - and so 'primes the pump'.
Composing melody - the hard bit! A song's melody is at least as important as any other component of your song. In fact, your audience probably won't bother listening to your song at all if your melody is weak. Articles and books can't tell you precisely how write a melody because if there was a formula it would be too valuable to share! Here are some of my experiences though:
- Noodling notes on a keyboard (even if you don't play properly, like me) can turn up interesting melodies. This doesn't work on a guitar, probably because of its bias towards chord playing, but playing chord changes on a guitar often enables you to 'hear' and then sing out a melody that's woven in those changes.
- Beware monotony: vary the range (high and low notes) of the melody to make it interesting. Don't fall into the common beginner's trap of composing a melody largely following the root notes of the chords; try and use other notes of the chords, or even ones not in the chord but suggested by it. Experiment by playing different chords under the same melody to see if that's more harmonically appealing. By experimenting like this you sometimes find it's an iterative process whereby your original melody changes for the better and the chords also change as you try different combinations.
- If you're stuck putting together a melody resist the urge to just change the chord - this won't substitute for lack of a clear melody line. Great songwriters seem to devise clever melodies using a few simple chords. Check out some of Brian Adams' big hits. He writes big, memorable rock songs around a handful of chords in what we guitarists call the first position, i.e. the easy chords that we all learn first like C, G, Ami, D, at the beginning of the fretboard. The most outstanding example of this is the Mavericks' 'Just Want to Dance the Night Away' whose verses, choruses and middle eight are all entirely different melodies sung over the same two alternating chords throughout the song - E and B7!
- Keep it simple: you're not writing an eight minute classical piece. If the postman can whistle it, then you've got a memorable and catchy melody. Pop music is a lot about repetition and a short, catchy melody can be made very effective by repetition, c.f. the verse lines in the Stones' '(I Can't Get No) Satisfaction'.
- Make a variation on the main melody in the middle eight, which is the portion of a song (usually eight bars long) that breaks things up just when it might become boring, e.g. the part in the Commodores' "Easy" that starts "I wanna be high, so high.." is the middle eight.