When a melody or line strikes you, record it asap!
I have dozens of garage band recordings that are nothing but a few lines here and there that come to me throughout the day.
You never know which one will turn into your next hit!
Same thing with lyrics.
Always have a notepad on hand so you can jot down words or ideas that might come while running errands or working.
I have found that you can’t turn creativity on or off, it will come whenever it feels like it, so be prepared!