Isn't that cute, you may hear as the puppy chews on your hand. Well guess what... not everyone finds it that cute and if not mitigated early, could become dangerous.
Puppies learn about biting and nipping as they play with their litter mates. Their litter mates also teach each other how far they can go with this by yelping when it hurts which startles the culprit into letting go.
We can co-opt this strategy by yelping "OW" when the puppy nips at us and withdrawing momentarily from the play session. Make sure the puppy is releasing and do not pull your hand away while she has hold of it, this could trigger the chase or tug instinct, which is opposite to what we are looking for. The goal here is to teach the puppy that gentle play continues; rough play stops.
Another strategy is to redirect the chewing or nipping to a chew or tug toy. The tug toy option allows the play session to continue without any skin being broken. Be careful that this does not get too aggressive though, it is an ideal time to teach "leave it" or "give" which can prevent problems later on.
Herding puppies tend to be "ankle biters". To mitigate ankle biting stop moving, when the puppy stops biting offer him an alternative toy as above. Treats are another option but use soft treats that can be an instant gratification, a biscuit or something similar take a few minutes to be consumed and the puppy will have forgotten why she got it.
Puppies and dogs for that matter do not understand "maybe" or "sometimes" . You must be consistent with this and all training for that matter.