The breed was developed by a tax collector to protect himself on his rounds, and this makes the Doberman one of the few dogs actually bred to accompany a person on walks. This gives you a definite advantage in training your Doberman puppy to walk well on a leash, but keep in mind that this is an active, energetic dog that will need to be well exercised if she is expected to walk gently with you on-leash.
To encourage walking nicely and to make walks a pleasant experience for your puppy, have her favorite treats and toys available. Use your particular Doberman puppy's personality to determine what sorts of rewards she will like best, but bring a variety in case this active dog loses interest in one or another. Determine early on what distance you would like your Doberman to walk at. Dobermans are very good heeling dogs, and if you would like a conformation heel, you can work with your puppy towards that, so long as she has plenty of off-leash exercise as well. If you would rather give your dog room to lope beside you on a flexilead, ensure that she is quick on a recall in case she should get too far from you. You don't want to have to reel in your Doberman puppy on a flexilead.