Rereading not only ferrets out problems, but it also ensures continuity of voice, as well as that elusive quality dear to both writers and rappers: flow. Constant rereading, which can be done out loud if you don’t trust your inner ear, is especially important now that progress has eliminated the tiresome but useful drudgery of retyping. Sometimes a glaring error that you motored blithely past a dozen times will become apparent only on the 13th read.
There are many more tips in the piece; take a look. Link via Jenny at Light Reading.