The board

The standard international dartboard is known as the "clock" board.  The standard dartboard measurement is 18 inches in diameter and has 20 numbered, pie-shaped segments of equal size, plus the bull's-eye.  Each numbered segment has a double ring on the outside perimeter of the scoring area and an interior triple ring (which count as double and triple of that number respectively).  The bull's-eye has an outer bull area (also known as the single bull, which scores 25) and an inner bull (also known as a double bull's-eye, which scores 50).

• Dart Board Height: 5 feet. 8 inches from floor to the center of the bull's-eye.
• Distance from front of the dartboard to the throwing line: 7 feet 9 1/4  inches 8 feet 0 inches for soft tip).  To mark the throw line a simple piece of tape will suffice.  Major tournaments, however, use a "hockey" which is a thin raised strip of wood approximately 1 1/2 inches high.
• Mounting:  Flush to the wall - not leaning like a picture - with the 20 at the top. 
• Location: Since darts often bounce out of the dartboard, never put a dartboard up near windows or breakables or where anyone could walk between the throw line and the dartboard.  Also, if you have a hard floor, such as concrete or wood, you may want to consider getting a dart mat.
• The dart scoreboard should be mounted to left or the right of the dart board for easy access.