See Hannah Montana's intended costume and then dress her up to match. To dress Miley, simply find an item in the bedroom or closet and click on it to pick it up. Drag the item onto Miley (seen on the right of the screen) Release the mouse over Miley to see her wear it. It's that simple!
Note: To change an item she's wearing, just choose another one and place it on her in the same way. The old item will simply reappear where you found it.