Hi Sam.I find it difficult to give tips on composing songs -- with or without lyrics(do you write lyrics?). I have no set way of doing it and every song is a different process. One thing I can say is to do it everyday if possible. For me, the more I write or play, the easier it is to come up with ideas(and the stronger those ideas are). Structure is also important to me. Maybe focus is a better word to use. I find that there is never a shortage of ideas. But I need to stay focused enough to put the ideas together. I need improvement in this ability. I've got enough for 3 or 4 new instrumentals but they are in little pieces at this point. I've also got quite a few lyrical songs on the go. This often means that none actually get done. Focus! Focus! Focus!
Organization helps too. Each new song I start gets a separate folder. Anything related to the song(i.e., notes, newspaper articles, etc) go into the folder.
One final tip -- read. There are a ton of books on songwriting and music theory that can help you. A new song will often develop when I sit down to learn one simple technique or idea. Theory that has recently helped me includes Jazz chords, chord substitution, flamenco techniques, and the list goes on.
Hope this helps. Jason LaPrade