If you've ever taken a class with me you have probably heard me say over and over again that we want to i) get the behaviour first and then ii) pair it with the word. I find a lot of people use the word "drop it" with their dogs without ever having done any training beforehand to teach the dog what drop it actually means.
I like to start this with a toy for a few reasons. First because I want to be able to give the object back as a reward; and secondly, I want the dog to feel like "drop it" is part of the game. It should never be taught with intimidation or by trying to scare the dog because as mentioned in Part I, this tends to make the dog defensive and you may end up causing your dog to guard. The point is to make the dog want to spit the item out happily.
Step 1 - Offer or toss the toy to entice the dog to pick it up in its mouth.
Step 2 - Once the dog is holding the toy, show the dog (let it sniff if need be) a high value (read: smelly & tasty) treat, and be ready to use your reward marker ("yes", "good", or a click if you are using a clicker) the moment the dog spits out the toy to take the treat.
Repeat Steps 1 & 2 until the dog is quickly spitting out the object as soon as the treat is presented.
Step 3 - Get your dog to take the toy again and add your cue (say "drop it") while you show the treat, still using your reward marker the moment the dog spits out the toy each time. You want to say "drop it" in a normal voice like you would say "sit" or any other cue. The point is to teach a word that can be used as an instruction; not to say it in a growly tone that might scare or intimidate your dog or be perceived as a threat.
Repeat Step 3 a few times and then try using your cue (drop it) without showing the treat right away, being ready to use your reward marker the moment the dog spits out the toy. If it does - great! That means the dog has associated the cue (drop it) with the behaviour (spitting the item out). You're ready to move on to Step 4.
Key Point: If it doesn't spit it out, don't keep repeating your cue. This means that the dog has not yet associated the cue with the behaviour yet, and repeating the cue will do nothing but make the dog start to ignore the word. You will need to practice Step 3 while separating the cue and prompt (showing the treat). What I mean by this is when you say "drop it", give the dog 1-2 seconds to think about/offer the behaviour before showing the treat to prompt the dog to drop the toy. Repeat this step until the dog starts to offer the behaviour (drop the toy) within 1-2 seconds of hearing the cue (drop it).
Step 4 - Now that your dog is spitting out the toy and expecting a treat, it's time to work on having the treat come later and from further away. You will still use your reward marker the moment your dog drops the item to mark the correct behaviour but the reward itself will start to come later. I usually start by having the treat in my pocket and practicing the drop it exercise, having the treat come out of my pocket once they have dropped the toy. Then I repeat the exercise having the treat come from the counter a step or two away from me, working up to getting the dog to drop the item with me going further away to get the treat. The idea here is to show the dog that the reward will come later or from further away. This is an important step if you want your dog to drop items when you don't have a treat in your hand!
Once your dog is doing this well, it's time to switch it up with some different variations of the game and make it more challenging. Here's where you can get creative, but here are some ideas that I've used with lots of success: