Answer:
There are many different kinds of Trance. Progressive and vocal are the most popular.
The basic elements of Trance start with a rise of a simple beat to a rolling beat of high hits to basslines to alternating beats. With in the back round a melody is on its way up, usually stings or a low "pluck". When things reach a certain point the beat drops and a smooth usually instrumental melody comes in. Slow strings kick up and begin a rise when usually a massive rise kicks into the main melody of the song with the height of the beat accompanying it. The song continues rising, usually theres a Piano loop with strings with a solid beat and a "hyper saw" melody before the song drops to its original beginning of the simple beat. Sometimes depending on the style of trance there will be vocals mixed in. With the low lyrics matching with the low point of the song
Songs like Tiesto - Ayla Ayla
Tiesto - Ten seconds to sun rise
System F - Out of the Blue (Giuseppe Ottaviani Remix - Armin van Buuren Edit)
are good examples of the different styles and different elements of Trance