Puppies learn about biting, and what's too hard and what's acceptable, from their mother and their littermates. When you bring your puppy home, the burden of teaching switches to your shoulders.
In addition to barking and house breaking, biting is a common problem when you first bring your toothy little darling home. It doesn't mean your puppy doesn't like you, it doesn't mean she's aggressive, and it doesn't mean she's spiteful. It's how puppies play, and it's how puppies interact with the world (though some use their paws too; Elka did. I imagine Boxers do too, if you can imagine such a thing.)
One good way to prevent your puppy razoring through your hands, feet, and clothing is redirection. When you see that mouth open (and puppies come with a set of 25 teeth, and then almost promptly start teething to get their grown up chompers in), give her something appropriate to chew on. Once your puppy is happily gnawing on a puppy-appropriate item instead of your precious body parts (don't worry, we'll talk about destructive chewing, and the mitigation thereof, a different day), praise your puppy. "Good chew" works, or "good girl", or "heck yeah!" Stay happy, stay positive, and remember, she doesn't really mean it. Or at least, not in the way that you think.
Always be very clear and very consistent with this. If it's okay to chew on your fingers sometimes, the next time it isn't okay, it'll be harder to change that habit. You don't want your grown dog chewing on you, don't let the puppy do it. The same applies to jumping (another future topic!). Set the adult rules for the puppy, and they'll be that much easier to train and enforce.
Puppies have a lot of energy, can be very focused and determined, and are little sponges; they want you to guide them and want you to teach them. Okay, sometimes they're just very focused and very determined, but we like the Utopian ideal of puppydom. If this was a perfect world, every dog would be biddable and want to please you. Every dog, and puppy, would have her eyes glued to your face, waiting with bated breath for your next cue. Well, those dogs exist, but we don't all end up with them. However, we can stay positive, and motivating, and give our puppies nudges into being these types of dogs.
The other method of bite inhibition that I suggest is rather more startling than redirection, and requires a certain fortitude on your part. As soon as you feel your puppies pearly whites on your flesh, you must yelp/exclaim as though your puppy has mortally wounded you. Immediately stop play. Leave the room or, if you can't exactly trust your puppy alone, turn your back, and remove all interaction for a short span of time, no more than a minute or two. After that time is up, resume play. Rinse, repeat.
"Yelping" rather than redirection worked for Elka, and worked quickly. To this day, the only time anybody has felt Elka's teeth, it has been accidental, wound-free, and while she was excited in play or while taking a treat. Really, I've suffered the most, giving her treats while clicker training on our walks, and even then, I've never suffered a "bite". Also, Elka doesn't much favor squeak toys, perhaps because of this aspect of her puppy days. On one hand, I feel a bit bad about that, as I know many dogs take great enjoyment in squeaky toys, and it really taps into their prey instinct, giving them a good energy outlet. On the other hand, squeaky toys really annoy me, so even if Elka did love them, her time with them would be severely limited. As it is, we have a few, and she gets time with them once in awhile, and then they go back on top of the fridge.