There's rarely a soup without the onion - so its best to perfect the dicing of one of soups most frequent starters.
Slice off the stem end, then clean any loose strands from the root end. Don't cut the root end off.
(Instructional videos on YouTube show chefs coring the stem and root ends with a paring knife - not necessary to dirty a second implement - just cleanly slice both ends.)
Half the onion through the two cut ends.
Now the peeling is easiest - peel the outer brown skin and the first inner layer together - they both come off easily with the help of the tip of a knife.
With the onion face down on your cutting board, make thin slices from the stem end almost the whole length of the onion to the root. Don't cut through the root end, though, or your onion will fall apart.
Last, make thin even slices perpendicular to the first cuts to achieve a fine dice.
Perfect, fast; no tears!