It's easy but can take time as all things can but it is all dependent on the learning skills of the dog.

I'll start right from the beginning and you only move on to the next step once the dog can carry out the current step 10 times without fail.

You will need:

A ball or toy equivalent.
Treats - these can be little bits of food or the toy itself.

The command to give for every stage is the word you want to use or you can just reward the action itself until the dog gets it. This best done indoors without distractions.

1). Command. Dog sniffs the object to retrieve. Reward.

2). Command. Dog takes the object from your hand. Reward given.

3). Command. Object dropped and dog sniffs it. Reward given.

4). Command. Object dropped and dog picks it up. Reward given.

5). Command. Object thrown 1m away. Dog sniffs and you move twoards dog. Reward given.

6). Command. Object thrown 1m away. Dog picks object up you move twords the dog. Reward given.

7). Command. Object thrown 1m away. Dog picks up the ball and comes to you for treat. Reward given.

8). Command. Distance increased.

9). Job done.

Depending how much the dog learns from each step depends on how fast the learning snowball effect will be. After the command you must wait for the dog to work it out though as this gets the snowball rolling a lot quicker.

You should move it to the garden next and when out on walks do not go to the dog if it has the toy. Wait tfor the dog to come to you to see why you are not playing. If you go to them they think you want waht they have and it becomes a chase game then. BAD idea and very tiring.