It is obvious for a person who has spent enough time in Net that though WEB-design has a graphic constituent in basis, it substantially differs from a print design. It is first of all caused by dynamic quality and interactive of web-page visual image. Almost any WEB-page has hyperlinks, navigation menu and other elements providing transitions between information units.
Interactive (requiring certain actions from user and reacting on them) elements distinguish electronic interfaces from well known book or newspaper. Naturally that at creation of magazine, reader’s actions on turning over the pages, folding down corners or inlaying of book-marks are not taken into account in its design.
In design of Web-page, those elements are the most important. Generally, development of competent arrangement of pages, logical site structure and navigation routes underlie web-design.
 For example, navigation panel, must be accessible (for that it is often duplicated above and at the bottom of page), simple in circulation and clear, it also must be compatible with  color and  geometrical conception of design.
So, how we already know graphic lie in basis of Web-design, but one should be very careful using it.
First of all abundance of graphic can cause irritation, especially if some of its elements contrast geometrically or not coincide in color gamut. Of coarse it is not always bad, but for using it one need certain knowledge in design psychology.
Secondly, graphic - are kilobytes, kilobytes - traffic, traffic - is time of loading. Not every visitor  is ready to wait  for a few minutes  to enjoy your graphic creation. Do not forget that Internet means first of all information.  

Thirdly, balance is graphic/texts   is very delicate thing. A text must be easy-to-read, and graphic insertions do not always assist it.
One of the greatest mistakes in WEB design is not using graphic or using of superfluous graphic. Designers are often too enthusiastic in page creation “look what I can do” forgetting about principles of pages functionality. Web-graphic should serve its majesty Function.  If the only function of graphic insertion  is original look,  it simply multiplies time of page loading. It takes more recourses and can push away impatient visitors.
So WEB-page design should suit following requirements: integrity of static and  dynamic constituents, logical interdependence of graphic and  text (  not talking about  multimedia video and  audio files), and of coarse  exclusiveness.

Below, you can see the types of graphic insertions in web-pages recommended to  the use.
The navigation buttons are used for the assisting visitors in moving on a site. Well designed, they are perceived easier than text links. Logotype is used for identification of corporate style. A logotype can substantially multiply knowable of brand or trade mark. The markers of lists are used for bringing in of visitors attention to the key points of documents. It is often used for the division of paragraphs and indentions in a document. Masthead gives visitors information about WEB-resource.  It also improves visual perception. Dividing lines are usually used for division of texts and facilitation of their perception.
Background pictures make look of the pages better. A horizontal two-color strip is used most often. The graphic heading allows usage independent from set on client computer fonts.
Photographs are often use for making page look more benevolent and original. The look of visitors in natural way is attracted to the photo images.
All graphic images on a site must correspond the chosen color gamut, used fonts and applied effects. For a professional web-site the minimum set of graphic consists of navigation, logotype, markers of lists and mastheads. If this graphic does not multiply time of page loading substantially, it is possible to add other elements. The optimum total size of web-page makes 40-60 Kb. Any additional graphic on a page must serve to the functions related to the subject and content of site.
In particular, designer firms lay out the examples of graphic works - so-called «portfolio». Illustrations can also serve to understanding of site sections. The clench of graphic files must not reduce quality of image.