What I do when I train my babies, is I ask for them to stop (say "whoa"). When they stop, I ask them to move their front feet out, by pulling gently to the side. As you are facing the horse, you pull slightly to your left for her right foot, and to your right for her left foot. When I do this I say "Out".
If she walks forward, or moves her back legs up, I back her up, and ask for just her front feet again.
When you start, even if she just moves her front feet forward half a step, stop and praise. She probably will not park out at first or very well, but if you can get her to start "giving you" her front feet when you pull her slightly, she will learn quickly.
When she has the idea of what your pulls mean, walk her around, stop, and park out. Walk around, stop, park out. Every time you stop, you should ask her to park out. Be consistent and don't get frustrated. Remember to always say "Whoa" and "Out".
Eventually, you will be able to just lift up on the lead rope and she will do it. I love it, I can get one of my yearlings this year to park out from the end of a long rope.
There ARE other ways to do this. Some methods include actually placing their feet for them with your foot. That is silly to me, because I am so used to my way.
Here is a topic that might help you: Teaching to park out - Trot.org Forums