Until they come up with insurance against bombing on stage, I will recommend my own remedy - mix it up. This won't stop you from bombing, but it may enable you to recover quickly. My advice is to do no more than 3 jokes on any topic and switch topics after every 3 jokes. Yes, another rule of threes. You have to keep in mind that different people like different jokes. You want to include enough variety that everyone will enjoy at least one joke. Call it "the salad bar method." I used to make each of my sets about a single topic, which proved disasterous when I peformed a set about blowjobs to a room of 20 middle-aged women. I had no idea that was going to be my audience, not that it matters. What matters is variety. Different jokes and different topics make all the difference.