From the book: Writing Without the Muse by Beth Baruch Joselow

Close your eyes and open a novel or book of short stories. Put your first finger on the page. Now open your eyes and record the sentence your finger has pointed out for you. That is your first sentence. Start writing. You are allowed three tries if the first sentence fate hands you is truly appalling. You may write either a poem or a story, whichever you feel most inspired to do.