Top the onion, and slice the onion in half.

Place it down.

Don't put your kinfe in like this.

Put it in on the side, and using this finger as a guide to place the knife in each time.

Make sure that the hand is like this.

That way you won't chop off your fingers because the knife runs off the finger.

The heel holds the whole onion together. You're not putting all the way through.

Slice all the way around score it through.

Holding the whole onion together, using your finger as a guide 'till slicing through.

When you get to the end, push the onion away, drop it down,

so that you can get these last bits of onion here.

Discard the stalk or use it in stocks.

So that's how to finely dice an onion.

If you want any more tips, then click on the link.