Screenwriting Crib Note #1

Unless you have secured a top-notch producer or you are the scion of the president of a music publishing company, don't script wall-to-wall modern hits or classic pop songs.  The music publishing costs could cost as much as the movie.  The days of when it could be done for cheaper like in American Graffiti or even The Bug Chill are gone.

Addendum to the note:  Don't make one particular song crucial to the plot (i.e. "They said goodbye at the San Francisco Bay, so their song HAS to be "(Sittin' on) The Dock of the Bay"); make sure that song can be replaced with something much cheaper. 

To wit:  a friend of mine was making a short film, and he scripted a rock band in the film break into a classic rock song.  He wanted to use "(I Can't Get No) Satisfaction."  Mind you, not The Rolling Stones version of it, just this fictional band's version of it, and only for about 20 seconds total.  The music publishing company wanted $100,000.  More than his entire budget.  No negotiations.   He settled on a Kinks' song for $500.

While songs give a great sense of mood, relaying on them too much in your script relays a lazy way to show mood.  Try it with your characters actions or dialogue, not what kind of musical taste they have.

And don't even think about scripting in Led Zepplin.  Unless you are Cameron Crowe, they usually say no.