A slightly different method I've started using with Dash (from a Suzanne Clothier seminar I attended):
Give the leash the amount of slack you her to have have (NOT the whole 6', more like 3-4') then stick the hand holding the leash partway into your pocket so I keep it at that length and am not tempted to pull on it.
Get her attention and give your loose-lead walking cue (most people use Let's Go) then start to walk, happy talking to be interesting and get keep attention. If she continues to stay nearby, you can praise her and pop a treat in her mouth every couple of steps so she knows you are very happy with what she's doing (the bonus being she wants to stay in treat-popping range

)
When she hits the end of the leash, stop, and resist the urge to verbally correct her or pull the leash.
When she turns around and actually pays attention to you (turning around to look at someone else doesn't count).. have a BIG party! "There you are, you remembered me, party for YOU!!" Be silly and shovel in a bunch of treats. Unless she has weight problems (or isn't food motivated.. not common in boxers!), it is far better to be generous w/treats than to be stingy.
Also institute
The Rule of "Even Though".. even though a bike just went by, even though she wants to sniff, even though she's excited because it's a new place. Even though these things may distract her and make her more likely to pull, still require her to behave and not pull on leash.
Later, when she's getting the idea of walking on a loose leash, you can also choose a release word to give when you are OK with her taking the full length of the leash and checking things out. You want to put this on cue so you can tell her *when* it's allowed and when it isn't.