To find something or get closer to something, you home in on it. To sharpen something is to hone it.
When you get closer to finding a difficult truth or finding a hiding criminal, you home in on them, just as a homing device allows you to find something.
Put an image in your mind of a homing pigeon arriving home to a lovely enclosure on top of a grand castle like the Windsor Castle or the Tower of London to remember that you home in on something.
A castle would be a great home, as long as it had modern heating and plumbing and wasn’t so big that you'd feel lonely. And you don’t want it to be so big that criminals could hide and then you’d have to home in on them with your homing pigeons. So maybe a small castle with a homing pigeon enclosure on the roof, just in case, would make a good safe home.
Here’s an example:
Aardvark quickly homed in on the weaknesses in Squiggly’s alibi.
Hone means to sharpen and comes from an Old English word that meant “stone” or “rock”—you hone a knife on a sharpening stone. Think of it as a honing stone to remember that to hone means to sharpen—it kind of rhymes and both words have an N.
You don’t hone in on anything except maybe a sharp blade.
Here is an example of the verb hone in a sentence:
Squiggly honed his cooking skills in Montreal.
If you think you’ll still have trouble remembering the difference between hone in and home in, the American Heritage Guide to Contemporary Usage and Style suggests using the phrase zero in as an alternative to home in.
Then I wondered where we get that phrase, and it appears to come from shooting culture. According to the American Heritage Dictionary of Idioms (those American Heritage people get around) to zero in on something means to direct your attention to it because when you aim a gun at something, you’re directing your attention on it.
The zero part comes from the crosshairs of you see through a scope, because if you’re aiming perfectly—directing all your attention so that the center of the crosshairs are on your target—you're at the point that looks just like the intersection of the X axis and Y axis on mathematical graphs, which is labeled (0,0). And that’s why directing your attention toward something, just like homing in on something, is called zeroing in on it.
And as a complete aside, I was asking my husband about guns and scopes while I was writing this, and he told me that originally the lines you see as crosshairs were made of spiderweb threads. That seemed too fascinating to be true to me, but from what I could find on the internet, it does appear to be true. Crosshairs were originally made using actual hair or spiderwebs.
So getting back to the Quick and Dirty Tip, to find something or get closer to something, you home in on it or zero in on it. You can remember to use home in by thinking of a homing pigeon on the roof of a castle. To hone something is different. It means to sharpen something, and to remember that, you can think of a honing stone for sharpening a knife.