How does a poem begin?
Thinking about the same thing over and over and over until it won’t go away. You think about something every day, usually a feeling, and at some point the feeling latches onto some kind of reality—something you saw or did or a person or an event. It could be anything. Then you feel and think about that for a long time—sometimes it’s weeks or months—then one day you just lie down or sit down and try to write it. If it doesn’t feel right you abandon it and go back to thinking about it again until you try to write again and learn how it feels. You do that until it feels right.
By feel right, I mean it doesn’t make you hate writing it. Or there is a sense of elation. I don’t really know. I can write something and say, This feels like a good poem because I’ve intellectually tackled this subject using what I believe is decent poetic craft. But that’s so unsatisfying, like eating a half-eaten meal.
If you begin a poem and it feels unsatisfying it’s probably because it is, and if it’s unsatisfying to you it will probably be to everyone else, and so you have to go back to thinking about it and trying to write it.