One of the most important things i've learned over the years is; developing your mindset in anything you do including song-writing.
Once i had that established with a hand-drawn mind map of how i would complete tasks as i am songwriting, i ensure i had my methodology in my mind and begin to do it with ease like it was natural.
One of the best tools that i came across over the years to help my when i am stuck is a tool that internet marketers use when they are writing articles, they use a spinner to get many variations of their article.
The spinner finds all kinds of synonyms for a word, and that's usually where i get stuck instead of using a frequent word or phrase that most song-writers use.
You will find what works for you when let it happen, practice, practice. It may start with a simple melody, it may start with a memory of an event, it may start with something you just made up. Once you develop your mindset and mindmap, you will discover that these melodies, phrase or stories will happen just about any time, even when you are sitting in the can.
The wife use to laugh at me when i was being creative, i would be in such a hurry to get back to my studio after coming out of the can, but i put a writing pad in there too.
what works for you is what is going to work for you.