Inspector16 has some good suggestions. But, before you follow them, make sure you really want a dog with a high level of play drive. If you are small and your dog is big, this can be too much to handle. Training fearful dogs to change emotional states into drive can be very effective. But, the more drive you make, the more control you need to have. If your dog is a sheltie, this is almost certainly good advice, as they are not very big and the vast majority are very easy to control. If your dog is an American bulldog, you could have a lot of difficulty controlling her as an adult once you "turn her on".
If you do think this kind of training will suit you both, I have a couple more suggestions. As adojrts says, practice leash training at home where she feels safe. I would also tie her on a 4 foot line in the house or the yard once or twice a day for a helf hour or so at a time, best at feeding time. Dogs that are tied up just a little bit learn to feel very comfortable with the leash behind them, they practice getting their legs untangled and they get less sensitive to accidental pulls or jerks from behind. I am not suggesting that you tie her for long periods, just enough that the leash is not an issue for her when you take her out.
Inspector16 suggests taking her right out the front door to play. It's possible that that will not work, as she knows the house is right behind her and she may only think about getting back inside. If that happens, carry her to the car and drive to the park. Initially you might carry her through the park to let her see and smell and hear the world. If she wants to get down, let her and then you follow her, even if that means just standing there, going nowhere. She leads, you follow. I would have a toy on a string (like a cat toy) and when she is looking fairly confident, bring it out and tease her with it. In the beginning she may not bite it, but if she is looking at it, that's great. Only bring it out for 20-30 seconds at a time, then put it away.
I would do this every day or a couple times a day. Within a week she should be chasing and playing with the toy. This is great, bc you are changing how she feels about going out. Now I would start on recalls, as Inspector16 suggested. I would do "restrained recalls". For this, you need two people who do not scare her. One person holds her and the other runs away and calls her. She should want to chase her person and catch them. If she does, the holder releases her and the runner stops and crouches down so she can come straight to them. You could reward with food, affection or toys her. The biggest part of the game is chasing you. If she likes both people equally, you can practice in both directions. If one is only a helper and not a close friend to her, then they should only act as holder. This is a great exercise for training recalls and building excitement and drive about the park and the handler. If you don't want her to jump on you when she gets there, make sure you hold treats or a toy at her nose level so that she has a "target" other than your face.
