Real stars don't fall or shoot across the sky. They are huge bodies of matter that have their own well defined orbits and position in space. What you are seeing, if you are lucky enough to spot a shooting star, is a piece of space debris that has entered the Earth's atmosphere and is burning up at a tremendous temperature.
These bits of debris usually come from disintegrating comets or asteroids and can vary in size from tiny specks of dust to larger rocks up to 10 metres in diametre. They are known as meteoroids and travel at speeds of between 11 km/sec to 72 km/sec. As a result of the massive friction created, the meteoroid burns up at over 1500 degrees Celsius, creating a trail of extremely bright light. While it is burning it is known as a meteor. On the very rare occasion, a meteor may not burn up completely and will hit the Earth creating a crater many times its size.
Times to see a shooting star
Much of the debris in space travel in clusters and enters the atmosphere at known times. These events are called meteor showers and you will see large numbers of meteors in the sky at one time. The exciting and much more romantic lone falling star is totally unpredictable and that is what makes it so special. So, keep an eye on the sky on a dark night, you never know when you may get to wish upon a falling star!