I call it the puzzle piece method. Akin to dumping all your legos out to see them all before you start building. Fill a page with just words and phrases that connect to your songs theme. Don’t hold back, just let whatever pops into your head come out. If it’s not good you won’t use it later but write it down anyway. Now the page is full and you can start fitting things together. Find a main idea or try and connect a few different ideas. If things aren’t fitting, find a different way to say it. Use a Thesaurus app along with RhymeZone.com to find the most fitting way to word it. It’s work but it’s fun and rewarding!