For Obi I just put a treat in front of his nose as I said "drop it" and he had to drop the object to take the treat from me. And also I tried not leaving things out that I didn't want him to have so that it didn't happen a lot, and when he did have something I didn't want him to have I didn't run at him and scream and make a big deal about it, I treated it as if he had something that fine, so I'd just casually walk towards him while asking him in a happy sort of voice "whatcha got there?" and then reach down, put the treat on his nose and say drop it.
I would also practice this with his toys, so I would give a treat and then give the toy back to him. That way he learnt that he wouldn't always lose the thing he wanted.
For Pixie I taught her while I was playing tug with her. I would get her excited and tug, and then stop and say "drop it", and then just grab her collar so she couldn't tug and then wait until she got bored (you can also stick a finger in her mouth and tickle the roof of her mouth if she won't let go). As soon as she let go we started tugging and having fun again. Within two minutes she was dropping the toy on command, and then it just took a bit more practise with other toys and objects for her to generalise the command, and that was it.
I always practise it while tugging, so they get lets of practise and most of the time dropping the toy results in more play, so the command is fun for them.
