A good read -
Songwriters on Songwriting by Paul Zollo (ISBN 978-0306812651). Though the process seems mysterious to many songwriters (or they don't want to give anything away to the opposition).
What I find interesting are the interviews with the Tin-pan Alley type songwriters who would write songs on commission and to order.
Don't be discouraged if it seems a struggle. Very few songwriters just churn them out all the time and in short order. Sometimes songs pop out of nowhere, fully formed. Often you have to slog away for months, sometimes years, until it's just right.
Remember the words of W.B. Yeats
A line will take us hours maybe;
Yet if it does not seem a moment’s thought,
Our stitching and unstitching has been naught.
Better go down upon your marrow-bones
And scrub a kitchen pavement, or break stones
Like an old pauper, in all kinds of weather;
For to articulate sweet sounds together
Is to work harder than all these …
… It’s certain there is no fine thing
Since Adam’s fall but needs much labouring.
Sometimes, it turns out, what sounds natural and flows beautifully took months of labour to sound so unforced and natural.
Look up "Songwriters on Songwriting" on Amazon, then look at the other suggestions. There's quite a few books that deal with this subject.
Keep on trying. I don't think there's a universal method.
Dylan: “My best songs are songs which were written very quickly. Yeah, very, very quickly. Just about as much time as it takes to write it down is about as long as it takes to write it.”
Cohen: “I am a working stiff. It takes me months and months of full employment to break the code of the song. To find out if there can be a song there.”
And often people were forced into it. The Rolling Stones were really a cover band at first. Andrew Oldham famously locked Jagger and Richards in a bathroom and told them they weren't going to be let out until they'd written a song.
