<p>How many pieces of music should I include, and what are the most common instruments?</p>
<p>I would include just a few of your very best. Adcoms aren't gonna waste their time with long CDs, especially if songs start getting mediocre.</p>
<p>I have no evidence for this, but I'd guess the most common instruments are piano, violin, trumpet, saxophone, and clarinet just because they are, in my experience, widely played.</p>
<p>They state that only applicants with unusual talent in a certain instrument should send in tapes. If it's very good, send it. Also, if it's a rarer instrument and good, that could help your case.</p>