Enter: The onion.
Onions are a total pain in the ... Meh. You get the idea. To us normal people, they make you cry. And cry some more. I already told you I'm not the Chef. I'm usually good now with the first half of the onion. But the 2nd half still comes out a little messy.
Here are some pics of how to do it right...
Straight up and down for the first part. Oh, if you can see: Rob's thumb is always at the back of the onion in these first 2 shots. He "pushes" the onion. It's almost as a means of control.
Now slice through the onion in horizontals... Maybe 2 or 3 of these. It's just gonna depend on how small you want your onions.
Hard Part: Now hold your onion (so it all doesn't start to spread out) and cut in full. Now you should start to have neat little onion pieces.
Use it for everything. It takes plenty of practise, and plenty more tears. But it's worth it if you don't want big chunks of onion in everything.