Which process do you follow to add lyrics to an existing melody?

When there is a melody already that you have to fill with words, I usually listen to it and my head already creates words and syllables that match the sound. So after listening and finding some words, I can then create a story around it. 

This can be a collaborative effort because sometimes the lyrics need tweaking to fit the melody.  If it is just a backing track following a chord progression, I began crafting a song to fit it.  Then, I start using the words of the lyric with that melody.

The process is a rinse-and-repeat, one where I repeat it several times until it all fits.  Then, I listen to see if it is too repetitive or wandering, and I use a vocal editor to tweak the melody if needed.  Lastly, I rerecorded the lyrics and melody for the finished product.

I usually listen to the instrumental track several times and then I record myself improvising the topline melody and lyrics over the music until I get a few lines that I like. From there I just start developing those ideas further to see if they're good enough for the song. If not, I just start improvising again and I repeat the process until I have at least one core idea that I'm happy with for the chorus and another one for the verses. That's usually enough to finish writing the song.