hmm.... i think if i'm writing lyrics for a song where the melody is already set, then it's a lot of trial and error to find words that fit while expressing the idea i want
but if i'm developing the lyrics and melody at the same time.... well it's a little more free-form but i guess it still requires trial and error because i have to make later verses i write fit the pattern of the earlier ones
i like looking up word rhymes on rhyme zone dot com to help me
another trick is 100% of my songs are either about love, or they're about the events of the video game that the song appears in, so i can just start writing lyrics without having to actually think of a theme first