I'd start indoors. First, put the leash on her and just let her drag it around the house. Get her used to the idea of wearing a leash.
Once she's used to the leash behind her, pick up the end. Don't try to guide her, just follow her around while holding the leash. If she doesn't want to move, just wait patiently until she gets going (in my experience, puppies can't stay still for very long!) and then follow her around. Once she's walking around without a problem, start guiding her. Encourage her to follow you by using some yummy treats.
For now, don't take her outside without her leash. When you're going outside, make a show of getting the leash and putting it on her. Once the leash is on, take her outside. You want her to learn that the leash means good things, and that she should be excited to see the leash.