I sometimes hear in interviews with musicians that their song ideas come to them suddenly and unexpectedly. When that moment comes, they often record their ideas on their mobile phones so as not to forget them and later turn them into a song. But this principle doesn't work for me at all. It has happened occasionally while walking on the street that a new song came into my head and I recorded one of the melodies with my mobile phone, but every time I listened to this recording later, my only thought was: "Why the hell did I record such crap, that sounds ridiculous ". Which is not surprising, because the one isolated, recorded melody has completely lost its meaning because it has been detached from the musical mood that I had in mind when I recorded it.
For me, the creation of a new song is far more than a short, spontaneous idea, but the product of previous thoughts and analysis of the previous songs. Before I start a new song I think about what went well in the previous song, what the song hadn't included and maybe should contain in the next song, and what I learned from the old song and could use for the next one without simply copying the old one.
The beginning of a song is often uncomfortable. I often play notes or harmony that are deliberately not very harmonious, just to tear myself out of the way of thinking of the last song. I then usually loop these new harmonies hundreds of times to see how they work and whether my changes are going in a positive direction or whether I should perhaps discard them. Only then do I start to compose additional melodies or rhythms on top of the starting harmonies, and then run them again hundreds of times in a loop to see whether they fit in ideally. Only then does the moment usually come when I suddenly feel that these ideas could become a great song, and the rest then almost happens automatically. Once this state is reached, all the catchy melodies emerge as if by themselves - no matter which key I press, everything sounds good because the musical foundation has been created.
But that doesn't always happen. With the first song that I wrote for the next album, this final state was not really reached, which is why I was not able to write a second part for it. In the unlikely event that something changes and I will be able to create a second part, this song will be on the new album. But it is much more likely that it will be replaced by a new song, as the musical ideas are just gushing out of me at the moment and all sound much better than the first one.