I work with special needs preschoolers, but the same techniques apply with any kids in this age group. We've found that very visual and very specific behavior charts work best. You also need to target a specific behavior or two rather that just say, "You need to behave." That's a big concept for preschoolers.
You can make a 1/2 sheet chart with 5 squares going across. At the top, put the desired behaviors, preferably in pictures. You can find pictures online or in magazines. The chart would say, "If I ... (show behaviors such as keep hands to self, use kind words, ride in stroller when requested, etc. - choose no more than two at a time). When you catch her doing something well, give her a sticker to put in one of the squares. Use words like, "You did a great job getting into your stroller when I asked you to. Here's a sticker for your chart. Only four more until you get a reward."
At the bottom of the chart, put a picture of the reward she's currently working for. You can have several rewards and rotate them. Let her choose which one to work for next, and only present the ones you want. For example, if she just worked for and earned ice cream, you wouldn't have that as a reward the next time. Rewards should be something you can give immediately when she earns it. So if it's an hour until lunchtime, you wouldn't want to make ice cream an option. You also wouldn't want to make a cupcake after dinner a reward if it's morning. That's too far away for her to think about. Rewards can be easy. It could be that she gets 10 minutes in a play area. She gets to choose the next attraction that you visit. It can be a choice from a grab bag of small, inexpensive toys you picked up at home. Or, less frequently, it can be ice cream or a treat. Put a picture of the reward she's working for at the bottom. You can mount the pictures on heavy paper, laminate them, and use Velcro to attach them so they can be used over and over.
One thing we don't do is take away anything they've earned. If she earns a sticker, you wouldn't take it away if she misbehaves. You just wouldn't give her another sticker and you would remind her why. "You can't earn stickers when you yell at me, refuse to ride in your stroller, etc." We find that positive systems work better. Once they get the hang of earning stickers and getting rewards, the negative behaviors gradually start to diminish. The important things are to 1) Decide which one or two behaviors to target at once, 2) Give her a sticker every time she makes a good choice regarding the targeted behaviors, and 3) Let her choose what reward she's working for and give her a visual reminder of that reward on the chart.
