One way to help visualize the relative sizes in the solar system is to imagine a model in which everything is reduced in size by a factor of a billion.
Then the model Earth would be about 1.3 cm in diameter (the size of a grape). The Moon would be about 30 cm (about a foot) from the Earth. The Sun would be 1.5 meters in diameter (about the height of a man) and 150 meters (about a city block) from the Earth.
Jupiter would be 15 cm in diameter (the size of a large grapefruit) and 5 blocks away from the Sun. Saturn (the size of an orange) would be 10 blocks away; Uranus and Neptune (lemons) 20 and 30 blocks away. A human on this scale would be the size of an atom but the nearest star would be over 40,000 km away.
Here are some great pictures showing the size of the earth in comparison to other objects in space.
Earth compared to the smaller planets (Venus, Mars, Mercury and Pluto):
Earth compared to the larger planets (Jupiter, Saturn, Uranus and Neptune):
The larger planets compared to the Sun:
Our Sun compared to Sirius, Pollux and Arcturus:
Sirius, Pollux and Arcturus compared to Rigel, Aldebaran, Betelgeuse
Watch this interesting video which shows the sizes of these objects