Every young puppy has an interest in playing and it is very easy to develop a pup's desire to play with a toy such as a ball or tug. This is often referred to as "toy drive". It is much more difficult to develop toy drive on an older dog that has no interest in playing, so it is always best to develop this drive while the dog is young and is always eager to play.
The first key is to have a "favourite toy" for your dog. If you play with your dog, try to use the same toy every time rather than using a different toy each time.