If all your standard remedies for hiccups don't seem to be having an effect, give one of these a try:
Breathe in and out of a paper bag to allow carbon dioxide to build up in your body. Do not use a plastic bag - this could be fatal.
Lie down with your head tilted as far back as possible and your mouth open.
Ask someone to gently press the protruding skin directly in front of your ear canals while you drink a glass of cold water.
Suck ice or drop a cold key or spoon down your back, inside your clothes.
Ask someone to surprise you by unexpectedly slapping your back.