Various studies have been undertaken over the years on music and focus, particularly when it comes to writing (and also, studying), and researchers have found that music sans lyrics is the most effective at keeping you on task and churning out meaningful words.
Don't go with Ravel’s Bolero or Pachelbel’s Canon.
It will lead to long, drawn out phrases and a certain repetition of information over and over again.
A great idea in a distracted environment is worthless to me.
But even a sorry idea can become a great piece if I can only find that zen-like focus that draws the words right out of me.