"Leash Manners" differs from "Heeling" in that when you are training Leash Manners your main goal is to teach your dog not to pull. Once you have instilled this in your dog, heeling is no big deal - just shorten up the lead and whala, he's heeling.

I've discovered if I don't put my puppies on leashes until we begin training for their NA Test (at 4-5 months old), I never have a problem with pulling. It takes me a bit of coaxing at first to get them to walk on the leash, but once we get passed that, we're off to a great start with leash manners.

I do understand not everyone has that option. Often puppies/dogs pull the hardest when they know where they are going, because they are excited to get there, such as to the park. You definitely want to discourage pulling, but since she is just 3 months old, negative corrections aren't really an option. For now, try this. Every time she pulls, turn around and walk her back a few steps the way you came. Then turn and resume your walk until she pulls, then repeat the procedure. It might take many repetitions for her to figure out she's not going to get where she wants to go if she pulls. Be patient and persistent. This method usually works.

Another good method, which you can do simultaneously with the above, is to treat your puppy over and over again if she is not pulling. She should learn it's beneficial to her (she gets paid) to walk nicely beside you. She should get zero from you (no hands, no treats, not talking) if she's pulling.