... of a first group (in the tonic key) and a second key (in the dominant, if major, or the relative major if in a minor key to start). The orchestral exposition would give the outline or the skeleton of the themes and the piece, and then when repeated by the soloist, they would change keys and give the full version with all the themes (minus the ritornello). The development section commonly starts with material that directly relates to the end of the exposition section, in order to make the move between the two sections smooth and joined, and you would rarely find a deliberate break or rest between the two. This section usually develops and explores themes form the exposition in a number of ways, e.g. sequential repetition, elaboration, ornamentation, fugato or elongation and often moves through a number of keys, unlike the exposition that usually transitions only once. Another common technique ...

See this essay or coursework document in full right now