So, "drop it" is important. It can keep your socks hole-free, keep a game of tug civil and controlled, protect your fingers while playing fetch, and keep your dog from consuming hazardous things like rocks and bottle caps and the like.
One method that's frequently related in books, that I think to be a good one, is to offer a trade. You can start with two identical toys. Play with your dog (or let your dog play with) one of the toys, and then after awhile, offer the "reserved toy" to get the toy out of the jaws of the beast. Identical or nearly identical is important here, not because the dog doesn't know the difference, but because the dog doesn't perceive it as a value change; you aren't taking anything away. You're offering one for the other.
The method I enacted was a sort of drop it/bring it hybrid. The object is always, of course, to get the object out of the puppy (or dog's) mouth without the dog consuming it. So, the time-honored method of exclaiming in a panic "What do you have?!" and chasing the dog until you catch her, only to find she's already swallowed it? Not so great. I can open Elka's mouth when I want to, and have done so to retrieve an object, but not after chasing her.
No, my "What do you have?" was in a cultivated, excited tone. I looked at puppy Elka and said "What do you have? Bring it here?" (not that she knew "bring" just yet, not formally), and clapped my hands and crouched for her, and she would run to me with it, and I would offer a treat for the object. This isn't to say Elka never chewed up anything she ought not (paper, pens, mechanical pencil, wooden pencil, edge of a hoodie hood.....) but to my knowledge, she never swallowed any of it.
I will warn you, once this is thoroughly engrained, there was a period of time where Elka would look for things to bring me. She would search the coffee table and the environs of the house, and looked very proud with each object she turned up. I once watched her nose a receipt off of the coffee table, and then hold it still with one paw while she scrunched it up with the other enough so that she could pick it up. She also once brought me a penny (!), which I did not see her pick up.
This was the stage at which we started to hand her empty cans or empty plastic bottles (lid on) and told her to "take it to the kitchen". So, just the object wasn't enough, there was taking it to the kitchen, and laying it in a hand for a treat, for it to go in the returns bin. Now, we can hand Elka and object and say "Take it to so and so" and she will deliver said object, unharmed, and with gusto. I once handed her a note in an old envelope to take downstairs to Jim, and she did.