Content
Content makes up the core of the message to be conveyed. It includes text, images, video, and other media. Good content is often the reason people come back to a site, because they find something useful, interesting or entertaining. Photos and videos should look professional and written content should be error free.
Design
Design is primarily used in reference to the visual presentation of content and truly defines the mood and feel of a website. Things like color choice, typography and layout style can all be used to give a true browsing experience. This helps to communicate the right message and provide users with a visual experience that compliments the contents of a website.
Usability
Usability refers to the way that users interact with data. Navigating a website should be quick, understandable and enjoyable. Internet is an interactive medium and users should be able to easily navigate a website.