Choosing random words or sentences is a fantastic way to begin writing when you're stuck for ideas. I once took a playwriting class that had us employ this technique to start a play. The teacher had us all write a page describing a place. When we were finished, we passed the description over to the person on our left. Next our teacher had us call out a series of objects, which he wrote on the chalkboard. When he'd compiled twenty or so items, he told us to pick two. Finally, he had us write on three slips of paper three things: a birthplace, a talent, and a physical characteristic. For each item he passed around a hat for us to put our slips in, and then passed the hat around again for us to take out a slip of paper, so that we each ended up with a birthplace, a talent, and a physical characteristic.
Our assignment was to write a two-character scene set in the place written for us by our classmate. One of the characters was to possess the three characteristics on those three slips of paper. Of the two objects we'd chosen from the board, one was to be the goal and one the obstacle of the scene. Our teacher supplied us with the opening and closing sentences.
I had a description of Bourbon Street in New Orleans; a good speller from Truth or Consequences, New Mexico who had big hands; a record player as the goal with the obstacle being an orange; the opening sentence "They were trying to make us think we'd met at some point," and the closing sentence "It's tragic to think that anyone reaches their potential at 35."
We had two weeks to write the scene. I put the assignment aside and continued work on a play already in progress. About four days later I woke up with the entire scene in my head. I'd never had that kind of experience--and haven't since--and I used the two object technique for the goals and obstacles for each scene of that play, Bourbon Street Spell, which went on to win first place in the 2005 Firehouse Theatre Festival in Richmond, Virginia.
Sometimes when I'm stuck on a piece of writing, I still employ writing prompts. I have an Apples to Apples Game