With the pointed end of the lemon facing up, cut an X into the side.
Here's the lemon cut along the X. This makes 4 pieces.
Cut each piece into half to end up with 8 wedges. You're all done.
Addended by request: The X cut is a good way to cut an oval shaped fruit evenly. I've also posted a different cutting procedure using the same method.
To cut a round large citrus, start by cutting it in half.
With the cut sides facing up, cut each half into half again. (If the fruit is very big so you can cut it into thirds.)
The wedges look like this from the sides. The fruit comes off the peel cleanly and is easy to eat.
Story Behind this Recipe
Everyone cuts lemons into 8 wedges lengthwise, but if you do it that way there's a high chance that the cut side of the wedges will be the sac wall...which means that when you squeeze the wedge, the juice goes flying everywhere. So I came up with this cutting method. I wanted to teach this method to my children, so I wrote it down here.
Lemons cut into 8 lengthwise wedges are fine, but since it takes the same amount of effort anyway, I like to go with this method, which results in nice cut sides. The walls of the lemon sacs won't be on the cut sides of the wedges, so the wedges are easy to juice and look beautiful too.