One of the things I’d be looking for in a new puppy, regardless of the breed is whether it’s confident or not. Confidence seems to me, to be largely genetic in dogs, and unconfident parents will lead to unconfident puppies. Generally speaking, good breeders will only breed from confident dogs.
A unconfident dog can have all sorts of issues,such as inappropriate responses and behaviours to stimuli. It’ll need a lot of work to make a good, reliable companion.
To start with, I’d take a puppy into a new environment, away from its littermates, and see how it behaves. A confident puppy will enjoy exploring the new area with it’s tail up, wagging. It should sniff objects and ideally physically interact with them. For example, putting front paws up on a chair to further investigate. A confident puppy should approach you and attempt to gain attention too.
Handle the puppy, stroke it, with long, deliberate strokes down it’s body, the puppy should relax and should enjoy the attention.
Expose the puppy to a sudden, unexpected noise, like dropping keys on the floor. A confident puppy will probably startle, but recover quickly and approach and investigates the keys (sniffing and/or pawing) without fear.
Finally, I’d see how keen the puppy is to accept training. Show the puppy some soft food treats, and give a couple to start, then move away. if the puppy quickly and enthusiastically approaches the food treats it’s a good sign, especially if it follows the food treats with his eyes and body. If the puppy initially doesn’t show any interest in food treats, try a squeaky toy.