When you hiccup, you are essentially sucking air in. That being said, the surest cure for hiccups is to prevent yourself from sucking in air. The only way I can do it, is to completely fill my lungs with air. I mean every last drop of air you can fit into your lungs. Partial measures will yield no success.
Fill your lungs with air and hold it as long as you can. I've never seen this method fail.
