The best way to avoid crying when dicing an onion is to use a very sharp knife and to move as quickly as safety permits.
Cut onions like a chef:
Step one: Cut off the end of the onion end with the small roots sticking out.
Step two: Cut it into half lengthwise, so that the end that is still together is cut into half.
Step three: Now remove the skin and may be one of the layers to clean the onion.
Step four: Holding your knife parallel to the cutting surface slice the onion parallel to the cutting surface so that you are making slices that are 1/4 inch from each other. Remember to never make a cut that would break through the end of the onion. The onion will come apart if you slice through the bottom end. Remember to never make a cut that would break through the end of the onion. The onion will come apart if you slice through the bottom end.
Step five: Turn the onion. Make lengthwise slices remembering not to cut all the way to the end. The onion will still be in one piece and look like half an onion.
Step six: Turn the onion and chop the onion all the way to the back of the part that is still together.
Step seven: You will have perfect small dices of onion. Now chop the other part of the onion the same way.