As a
songwriter myself (of sorts - for an example of my poor attempts at songwriting see
Do What You Will) I thought this nodeshell was as good a place as any to put my thoughts on how to start writing songs. (This node assumes you know at least the basics of playing one instrument. If not,
guitar is the easiest to learn). This node will concentrate on writing music, as I am not a particularly proficient lyricist - see
How to write lyrics for better advice than I could give on that.
First, learn the very basics of music notation. Yes, we all know Paul McCartney cannot read or write sheet music - guess what? You're not Paul McCartney. No-one's saying you should do a degree course in music theory - though that certainly won't hurt - but learn the basics.
Once you've done this, get a few books of sheet music - doesn't have to be full scores, fake books are quite acceptable - of songwriters who are either your favourites or who are generally considered to be 'great' songwriters. The Beatles Complete is a good choice for a fake book, or, in areas where it's available (due to copyright restrictions sheet music can vary from area to area) The Concise Beach Boys. Note however that many fake books have horrendously oversimplified chords in them - Beach Boys ones are particularly bad for this, many replacing the 9th chord in California Girls with a 5th or 7th - so if possible play one or two songs in the music store to check they sound right.
Now, learn at least 30 songs, by at least four or five different writers, in different genres, that you think are great. Learn these so they become second nature, like riding a bike. The reason for this is the same as learning scales as a player - you want to be able to automatically move to chord changes that you can hear in your head, without having to think about it.
Next, a simple exercise. Look at the sheet music for your very favourite song, and try to pick out the hook. What the hook is can vary enormously from song to song, but generally in a good song (as opposed to merely a good record) it will be the point in which the song varies from a standard pattern - maybe a key change or a bar with a different number of beats.
An example would be a technique used in both The Beatles' Day Tripper and the Beach Boys' The Warmth Of The Sun (by John Lennon/Paul McCartney and Brian Wilson/Mike Love respectively). Both these songs start with an absolute standard set of changes (12-bar blues for Day Tripper, I-vi-ii-V7 for The Warmth Of The Sun) but then halfway through that pattern change key and start the pattern again, then halfway through changes back. To make this clearer, the standard pattern of changes for a I-vi-ii-V7 song such as Blue Moon or Heart And Soul is:
In C - C-Am-Dm-G7
In Eb - Eb-Cm-Fm-Bb7
Meanwhile, the chords for Warmth Of The Sun are:
C-Am-Eb-Cm-Dm-Dm(held for two bars)-G7-Gaug7
The equivalent of the change to Eb in the Beatles song is to the II7 chord on the line 'She was a DAY tripper'.
Anyway, find out where the hook is, and try using the idea of that hook in a new context. For example you might try using the idea of a key change in the middle of a well known sequence used above, but try it on a cliched I-IV-V-IV sequence (the Louie Louie/La Bamba/Hang On Sloopy/Twist & Shout/Wild Thing changes) rather than the changes for a doo-wop ballad or a blues rocker.
Of course, most well written songs will have several of these hooks in them, and you have to be able to come up with your own. The best way to do that is to have a large repertoire of chords at your disposal (I can't count the number of times Ddim7 has helped me through an awkward key change) and to be able to write a good strong melody over the top. Of course inspiration is the most important thing, but in songwriting as much as (possibly even more than) any other creative field, this has to be backed up with a good toolkit.
Obviously one writeup can't even scratch the surface of this subject - a beginning songwriter really needs a manual in order to learn (other than by experience). Luckily such a book does exist - Tunesmith by Jimmy Webb is a book I wish I'd read when I was starting to write songs. It's the only book I've ever read that explains the actual mechanical process of songwriting in such a way that a total beginner with no previous experience could sit down and write a good, interesting song, by just following his instructions.
Another good book on the subject is Songwriters On Songwriting by Paul Zollo. This doesn't describe the technical process very well, but by interviewing huge numbers of great songwriters (primarily American) he manages to explain the mindset of songwriters very well - this book resonates a lot with almost ever songwriter I've spoken to, and when I e-mailed Van Dyke Parks (one of the interviewees) asking for advice, his principal piece of advice was simply to read Songwriters On Songwriting.
arrogantsob's w/u is right on the nail too. My advice here is just showing the method I started from, but the method below works equally well, and is the method described in Tunesmith . My own technique is to write a song from a melody I hear in my head, but I can usually automatically harmonise that melody because I've built up my repertoire of chords over the years. YMMV