When creating a responsive design you need to ensure that the site is flexible enough to deal with phone, tablets and PCs. The site should be based on a fluid grid so that when the screen size changes the elements on the page re-order themselves accordingly.
You also need to determine which elements on the page are crucial to your mobile visitors. For example, a moving slider looks great on a PC but do mobile users need to see it? Generally responsive sites 'hide' most of the unwanted elements, leaving the mobile visitor with access to just the sections they are interested in.