Great thread Sandie!
I have never formally studied any methods for songwriting, having said that, I am very interested and passionate about the subject, and these days I spend a significant amount of my guitar practice time dedicated to songwriting and coming up with new ideas for songs. Sometimes this happens easily, other times I don't feel overly creative. In the latter instance I take the opportunity to work on more structured practice items like scales and arpeggios, rhythm etc.
When I am feeling very inspired and creative I find it hard to practice the more clinical things like technique and scales. I keep trying to find a good balance!
A few things that have helped me with songwriting over the years.
1. Changing my mentality from trying to 'perfect' everything to trying to 'complete' everything. This helped me actually write complete songs rather than just a bunch of independent riffs none of which I was completely happy with.
2. Ear training. I have improved this over the years and it has helped me express myself more easily and accurately, which is very important for songwriting.
3. Interacting with other songwriters. I learned a lot from getting to know other songwriters in my local area through jam sessions, gigs and muso nights.
In my experience, other songwriters can be a great source of advice and inspiration for your own songwriting.
4. Recording all my own ideas. You must do this otherwise you will most probably forget many of your ideas before completing a song. It's a great way to archive ideas if you need to come back to them in the future. I could go on and on about the benefits of recording your own musical ideas, so if you don't already do it, you should start now!